Compact semiconductor memory device having reduced number of contacts, methods of operating and methods of making

ABSTRACT

An integrated circuit including a link or string of semiconductor memory cells, wherein each memory cell includes a floating body region for storing data. The link or string includes at least one contact configured to electrically connect the memory cells to at least one control line, and the number of contacts in the string or link is the same as or less than the number of memory cells in the string or link.

CROSS-REFERENCE

This application is a continuation of application Ser. No. 16/239,758,filed on Jan. 4, 2019, which is a continuation of application Ser. No.16/045,630, filed on Jul. 25, 2018, now U.S. Pat. No. 10,204,908, issuedon Feb. 12, 2019, which is a continuation of application Ser. No.15/892,236, filed on Feb. 8, 2018, now U.S. Pat. No. 10,056,387, issuedon Aug. 21, 2018, which is a continuation of application Ser. No.15/616,369, filed on Jun. 7, 2017, now U.S. Pat. No. 9,922,981, issuedon Mar. 20, 2018, which is a continuation of application Ser. No.15/428,921, filed on Feb. 9, 2017, now U.S. Pat. No. 9,704,870, issuedon Jul. 11, 2017, which is a continuation of application Ser. No.15/185,156, filed on Jun. 17, 2016, now U.S. Pat. No. 9,601,493, issuedon Mar. 21, 2017, which is a continuation of application Ser. No.14/856,943, filed on Sep. 17, 2015, now U.S. Pat. No. 9,391,079, issuedon Jul. 12, 2016, which is a continuation of application Ser. No.14/637,688, filed on Mar. 4, 2015, now U.S. Pat. No. 9,209,188, issuedon Dec. 8, 2015, which is a continuation of application Ser. No.14/177,819 filed on Feb. 11, 2014, now U.S. Pat. No. 9,001,581, issuedon Apr. 7, 2015, which is a continuation of application Ser. No.13/941,227 filed on Jul. 12, 2013, now U.S. Pat. No. 8,711,622, issuedon Apr. 29, 2014, which is a continuation of application Ser. No.12/897,528 filed on Oct. 4, 2012, now U.S. Pat. No. 8,514,622, issued onAug. 20, 2013, which claims the benefit of U.S. Provisional ApplicationNo. 61/309,589, filed on Mar. 2, 2010. We hereby incorporate all of theaforementioned applications and patents herein, in their entireties, byreference thereto, and we claim priority to application Ser. Nos.16/239,758; 16/045,630; 15/892,236; 15/616,369; 15/428,921; 15/185,156;14/856,943; 14/637,688; 14/177,819; 13/941,227; and 12/897,528 under 35USC § 120. We further claim priority to U.S. Provisional Application No.61/309,589 under 35 USC § 119.

This application claims the benefit of U.S. Provisional Application No.61/309,589, filed Mar. 2, 2010, which application is hereby incorporatedherein, in its entirety, by reference thereto and to which applicationwe claim priority under 35 U.S.C. Section 119.

Application Ser. No. 12/897,528 was filed on even date with applicationSer. No. 12/897,538 filed on Oct. 4, 2010, now U.S. Pat. No. 8,264,875which issued on Sep. 11, 2012 and application Ser. No. 12/897,516 filedon Oct. 4, 2010. Both application Ser. Nos. 12/897,528 and 12/897,516are hereby incorporated herein, in their entireties, by referencethereto.

FIELD OF THE INVENTION

The present invention relates to semiconductor memory technology. Morespecifically, the present invention relates to a semiconductor memorydevice having an electrically floating body transistor.

BACKGROUND OF THE INVENTION

Semiconductor memory devices are used extensively to store data. Staticand Dynamic Random Access Memory (SRAM and DRAM) are widely used in manyapplications. SRAM typically consists of six transistors and hence has alarge cell size. However, unlike DRAM, it does not require periodicrefresh operation to maintain its memory state. Conventional DRAM cellsconsist of one-transistor and one-capacitor (1T/1C) structure. As the1T/1C memory cell feature is being scaled, difficulties arise due to thenecessity of maintaining the capacitance value. DRAM based on theelectrically floating body effect has been proposed (see for example “ACapacitor-less 1T-DRAM Cell”, S. Okhonin et al., pp. 85-87, IEEEElectron Device Letters, vol. 23, no. 2, February 2002 and “MemoryDesign Using One-Transistor Gain Cell on SOI”, T. Ohsawa et al., pp.152-153, Tech. Digest, 2002 IEEE International Solid-State CircuitsConference, February 2002). Such memory eliminates the capacitor used inconventional 1T/1C memory cell, and thus is easier to scale to smallerfeature size. In addition, such memory allows for a smaller cell sizecompared to the conventional 1T/1C memory cell.

There is a continuing need for semiconductor memory devices that aresmaller in size than currently existing devices.

The present invention meets the above need and more.

SUMMARY OF THE INVENTION

In one aspect of the present invention, an integrated circuit isprovided that includes a link or string of semiconductor memory cells,wherein each memory cell comprises a floating body region for storingdata; and the link or string comprises at least one contact configuredto electrically connect the memory cells to at least one control line,wherein the number of contacts is the same as or less than the number ofthe memory cells.

In at least one embodiment, the number of contacts is less than thenumber of memory cells.

In at least one embodiment, the semiconductor memory cells are connectedin series and form the string.

In at least one embodiment, the semiconductor memory cells are connectedin parallel and form the link.

In at least one embodiment, the integrated circuit is fabricated on asilicon-on-insulator (SOI) substrate.

In at least one embodiment, the integrated circuit is fabricated on abulk silicon substrate.

In at least one embodiment, the number of contacts is two, and thenumber of semiconductor memory cells is greater than two.

In at least one embodiment, the memory cells further comprise first andsecond conductive regions interfacing with the floating body region.

In at least one embodiment, the first and second conductive regions areshared by adjacent ones of the memory cells for each the memory cellhaving the adjacent memory cells.

In at least one embodiment, each memory cell further comprises first,second, and third conductive regions interfacing with the floating bodyregion.

In at least one embodiment, each memory cell further comprises a gateinsulated from the floating body region.

In at least one embodiment, at least one of the memory cells is acontactless memory cell.

In at least one embodiment, a majority of the memory cells arecontactless memory cells.

In at least one embodiment, the memory cells store multi-bit data.

In another aspect of the present invention, an integrated circuit isprovided that includes a plurality of contactless semiconductor memorycells, each semiconductor memory cell including: a floating body regionfor storing data; first and second conductive regions interfacing withthe floating body region; a gate above a surface of the floating bodyregion; and an insulating region insulating the gate from the floatingbody region.

In at least one embodiment, the contactless memory cells are connectedin series.

In at least one embodiment, the contactless memory cells are connectedin parallel.

In at least one embodiment, the integrated circuit comprises at leastone semiconductor memory cell having at least one contact, a totalnumber of the contacts being less than a total number of memory cellsthat includes a total number of the memory cells having at least onecontact and a total number of the contactless memory cells.

In another aspect of the present invention, an integrated circuit isprovided that includes: a plurality of semiconductor memory cellsconnected in series, each semiconductor memory cell comprising: afloating body region for storing data; first and second conductiveregions interfacing with the floating body region; a gate above asurface of the floating body region; and an insulating region insulatingthe gate and the floating body region.

In at least one embodiment, at least one of the semiconductor memorycells is a contactless semiconductor memory cell.

In at least one embodiment, the at least one contactless semiconductormemory cell comprises a third conductive region interfacing with thefloating body region.

In another aspect of the present invention, an integrated circuit isprovided that includes a plurality of semiconductor memory cellsconnected in parallel, each semiconductor memory cell comprising: afloating body region for storing data; a conductive region interfacingwith the floating body region; a gate above a surface of the floatingbody region; and an insulating region insulating the gate from thefloating substrate region; wherein at least one of the semiconductormemory cells is a contactless semiconductor memory cell.

In at least one embodiment, a majority of the semiconductor memory cellsare contactless semiconductor memory cells.

In at least one embodiment, the integrated circuit comprises a number ofcontacts, the number being less than or equal to a number of the memorycells.

In at least one embodiment, the memory cells each further comprise asecond conductive region interfacing with the floating body region.

In at least one embodiment, the memory cells each further comprisesecond and third conductive regions interfacing with the floating bodyregion.

In another aspect of the present invention, an integrated circuit isprovided that includes a plurality of contactless semiconductor memorycells connected in parallel, each semiconductor memory cell comprising:a floating body region for storing data; first and second conductiveregions interfacing with the floating body region; a gate above asurface of the floating region; and an insulating region insulating thegate and the floating body region.

In another aspect of the present invention, an integrated circuit isprovided that includes: a memory string or link comprising a set ofcontactless semiconductor memory cells; and a first contact contacting afirst additional semiconductor memory cell; wherein the contactlesssemiconductor memory cells are accessible via the first contact.

In at least one embodiment, the integrated circuit further includes asecond contact contacting a second additional semiconductor memory cell;wherein the contactless semiconductor memory cells are accessible viathe second contact.

In at least one embodiment, the contactless semiconductor memory cellsand the additional semiconductor memory cell are connected in series.

In at least one embodiment, the memory string or link comprises a firstmemory string or link and the set comprises a first set, the integratedcircuit further comprising: a second memory string or link comprising asecond set of contactless semiconductor memory cells; and a secondcontact contacting a second additional semiconductor memory cell;wherein the second set of contactless semiconductor memory cells areaccessible via the second contact.

In at least one embodiment, the memory string or link comprises a firstmemory string and the set comprises a first set, the integrated circuitfurther comprising: a second memory string comprising a second set ofcontactless semiconductor memory cells; a third contact contacting athird additional semiconductor memory cell; and a fourth contactcontacting a fourth additional semiconductor memory cell; wherein thesecond set of contactless semiconductor memory cells are accessible viathe third and fourth contacts; wherein the first set of contactlesssemiconductor memory cells, the first additional semiconductor memorycell and the second additional semiconductor memory cell are connectedin series, and wherein the second set of contactless semiconductormemory cells, the third additional semiconductor memory cell and thefourth additional semiconductor memory cell are connected in series inthe second string.

In at least one embodiment, the integrated circuit further includes afirst terminal connected to the first contact and the third contact; asecond terminal connected to the second contact; and a third terminalconnected to the fourth contact.

In at least one embodiment, the semiconductor memory cells comprisesubstantially planar semiconductor memory cells.

In at least one embodiment, the semiconductor memory cells comprisefin-type, three-dimensional semiconductor memory cells.

In at least one embodiment, the first set of contactless semiconductormemory cells are aligned side-by side of the second set of contactlesssemiconductor memory cells; the first string comprises a first set ofinsulation portions that insulate adjacent memory cells in the firststring, and a second set of insulation portions that insulate the memorycells in the first string from adjacent memory cells in the secondstring; and the second string comprises a third set of insulationportions that insulate adjacent memory cells in the second string, and afourth set of insulation portions that insulate the memory cells in thesecond string from adjacent memory cells in the first string.

In at least one embodiment, the first and second contacts are located atfirst and second ends of the memory string.

In at least one embodiment, each semiconductor memory cell comprises: afloating body region for storing data; first and second conductiveregions interfacing with the floating body region; a gate above asurface of the floating region; an insulating region insulating the gatefrom the floating body region; and a word line terminal electricallyconnected to the gate.

In another aspect of the present invention an integrated circuitincludes a plurality of floating body memory cells which are linkedeither in series or in parallel. The connections between the memorycells are made to reduce the number of contacts for the overall circuit.Because several memory cells are connected either in series or inparallel, a compact memory array is provided.

These and other features of the invention will become apparent to thosepersons skilled in the art upon reading the details of the integratedcircuits, strings, links memory cells and methods as more fullydescribed below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a memory cell in accordance with anembodiment of the present invention.

FIG. 2A schematically illustrates a memory array having a plurality ofmemory cells according to an embodiment of the present invention.

FIG. 2B schematically illustrates a memory array having a plurality ofmemory cells, with read circuitry connected thereto that can be used todetermine data states, according to an embodiment of the presentinvention

FIG. 3 shows exemplary bias conditions for reading a selected memorycell, as wells as bias conditions of unselected memory cells in a memoryarray according to an embodiment of the present invention.

FIG. 4A shows exemplary bias conditions for reading a selected memorycell according to an embodiment of the present invention.

FIGS. 4B-4D illustrate bias conditions on unselected memory cells duringthe exemplary read operation described with regard to FIG. 3, accordingto an embodiment of the present invention.

FIG. 5 schematically illustrates and example of a write “0” operation ofa cell according to an embodiment of the present invention.

FIGS. 6A-6B show an example of bias conditions of selected andunselected memory cells during a write “0” operation according to anembodiment of the present invention.

FIG. 7 illustrates bias conditions for cells in an array during a write“0” operation in which all memory cells sharing the same BL terminal arewritten into state “0” according to an embodiment of the presentinvention.

FIG. 8 illustrates bias conditions for selected and unselected memorycells of a memory array for a write “0” operation according to analternative embodiment of the present invention.

FIG. 9A illustrates bias conditions of the selected memory cell underthe write “0” operation described with regard to the example of FIG. 8.

FIGS. 9B-9D illustrate examples of bias conditions on the unselectedmemory cells during write “0” operations described with regard to theexample shown in FIG. 8.

FIGS. 10 and 11A illustrate an example of the bias conditions of aselected memory cell under a write “1” operation using band-to-bandtunneling according to an embodiment of the present invention.

FIGS. 11B-11D show examples of bias conditions of the unselected memorycells during write “1” operations of the type described with regard toFIG. 10.

FIG. 12 schematically illustrates bias conditions on memory cells duringa write “1” operation using impact ionization according to andembodiment of the present invention.

FIGS. 13A-13D and 14 illustrate an example of the bias conditions of theselected memory cell 50 under a write “1” operation using an impactionization write “1” operation according to an embodiment of the presentinvention.

FIG. 15 illustrates a prior art arrangement in which adjacent memorycells share common contacts.

FIG. 16A shows a cross-sectional schematic illustration of a memorystring according to an embodiment of the present invention.

FIG. 16B shows a top view schematic illustration of a memory cell arrayincluding two strings of memory cells between the SL terminal and BLterminal according to an embodiment of the present invention.

FIG. 17 shows an equivalent circuit representation of the memory arrayof FIG. 16B.

FIGS. 18 and 19A-19B illustrate bias conditions during a read operationaccording to an embodiment of the present invention.

FIGS. 20-21 illustrate bias conditions during a write “0” operationaccording to an embodiment of the present invention.

FIGS. 22A-22B illustrate bias conditions during a write “0” operationthat allows for individual bit writing according to an embodiment of thepresent invention.

FIGS. 23A-23B illustrate bias conditions during a band-to-band tunnelingwrite “1” operation according to an embodiment of the present invention.

FIGS. 24A-24B illustrate bias conditions during an impact ionizationwrite “1” operation according to an embodiment of the present invention.

FIG. 25A schematically illustrates a fin-type, three-dimensional memorycell according to an embodiment of the present invention.

FIG. 25B schematically illustrates a fin-type, three-dimensional memorycell according to another embodiment of the present invention.

FIG. 26 schematically illustrates a memory cell fabricated on a bulksubstrate according to an embodiment of the present invention.

FIG. 27A schematically illustrates n-p-n bipolar devices formed by theburied well region, floating body, and SL and BL regions of the memorycell of FIG. 26 according to an embodiment of the present invention.

FIG. 27B shows an energy band diagram of the intrinsic n-p-n bipolardevice of the cell of FIG. 26 when the floating body region ispositively charged and a positive bias voltage is applied to the buriedwell region according to an embodiment of the present invention.

FIG. 27C shows an energy band diagram of the intrinsic n-p-n bipolardevice of the cell of FIG. 26 when the floating body region 24 isneutrally charged and a bias voltage is applied to the buried wellregion according to an embodiment of the present invention.

FIG. 28 schematically illustrates bias conditions on memory cells duringa read operation of a selected memory cell according to an embodiment ofthe present invention.

FIG. 29 schematically illustrates bias conditions on memory cells duringa write “0” operation according to an embodiment of the presentinvention.

FIG. 30 schematically illustrates bias conditions on memory cells duringa write “0” operation according to another embodiment of the presentinvention.

FIG. 31A schematically illustrates an example of bias conditions of aselected memory cell under a band-to-band tunneling write “1” operationaccording to an embodiment of the present invention.

FIG. 31B shows bias conditions of selected and unselected memory cells150 during an impact ionization write “1” operation according to anembodiment of the present invention.

FIG. 32A shows a cross-sectional schematic illustration of a memorystring according to an embodiment of the present invention.

FIG. 32B shows a top view schematic illustration of a memory cell arrayincluding two strings of memory cells between the SL terminal and BLterminal according to an embodiment of the present invention.

FIG. 32C shows an equivalent circuit representation of a memory arraythat includes strings shown in FIG. 32B as well as additional strings,in accordance with an embodiment of the present invention.

FIG. 33 shows bias conditions on a memory string during a read operationaccording to an embodiment of the present invention.

FIG. 34A illustrates bias conditions on a selected memory cell as wellas unselected memory cells in the same and in other strings, during aread operation according to an embodiment of the present invention.

FIG. 34B illustrates the array of FIG. 34A with read circuitry attachedto measure or sense the current flow from the BL terminal to the SLterminal in regard to the selected cell, according to an embodiment ofthe present invention.

FIG. 35 shows bias conditions on a memory string during a write “0”operation according to an embodiment of the present invention.

FIG. 36 illustrates bias conditions on a selected memory cell as well asunselected memory cells in the same and in other strings, during a write“0” operation according to an embodiment of the present invention.

FIG. 37 shows bias conditions on a memory string during a write “0”operation that allows for individual bit writing according to anembodiment of the present invention.

FIG. 38 illustrates bias conditions on a selected memory cell as well asunselected memory cells in the same and in other strings, during a write“0” operation that allows for individual bit writing according to anembodiment of the present invention.

FIG. 39 shows bias conditions on a memory string during a band-to-bandtunneling write “1” operation according to an embodiment of the presentinvention.

FIG. 40 illustrates bias conditions on a selected memory cell as well asunselected memory cells in the same and in other strings, during aband-to-band tunneling write “1” operation according to an embodiment ofthe present invention.

FIG. 41 shows bias conditions on a memory string during an impactionization write “1” operation according to an embodiment of the presentinvention.

FIG. 42 illustrates bias conditions on a selected memory cell as well asunselected memory cells in the same and in other strings, during animpact ionization write “1” operation according to an embodiment of thepresent invention.

FIG. 43 schematically illustrates a fin-type, three-dimensional memorycell according to an embodiment of the present invention.

FIG. 44 schematically illustrates a fin-type, three-dimensional memorycell according to another embodiment of the present invention.

FIG. 45A schematically illustrates a top view of two strings of memorycells in a memory array according to an embodiment of the presentinvention.

FIG. 45B is a cross-sectional view of a string from the arrayillustrated in

FIG. 45A.

FIGS. 46A-46U illustrates various stages during manufacture of a memoryarray according to an embodiment of the present invention.

FIG. 47 schematically illustrates a link of memory cells connected inparallel according to an embodiment of the present invention.

FIG. 48A schematically illustrates a top view of a memory cell of thelink of FIG. 47.

FIG. 48B is a sectional view of the memory cell of FIG. 48A taken alongline I-I′ of FIG. 48A.

FIG. 48C is a sectional view of the memory cell of FIG. 48A taken alongline II-II′ of FIG. 48A.

FIG. 49 shows an equivalent circuit representation of a memory arraythat includes the link of FIG. 47, according to an embodiment of thepresent invention.

FIG. 50 is a schematic illustration of an equivalent circuit of a memoryarray of links in which a read operation is being performed on aselected memory cell of one of the links according to an embodiment ofthe present invention.

FIG. 51 schematically illustrates the selected memory cell of the arrayrepresented in FIG. 50 and bias conditions thereon during the readoperation.

FIG. 52 is a schematic illustration of an equivalent circuit of a memoryarray in which a write “0” operation is being performed on a selectedlink of the array according to an embodiment of the present invention.

FIG. 53 schematically illustrates a memory cell of the link representedin FIG. 52 that is having a write “0” operation performed thereonaccording to an embodiment of the present invention.

FIG. 54 is a schematic illustration of an equivalent circuit of a memoryarray in which a write “0” operation is being performed according to analternative embodiment of the present invention.

FIG. 55 schematically illustrates a memory cell of the array representedin FIG. 54 that is having a write “0” operation performed thereonaccording to the alternative embodiment described with regard to FIG.54.

FIG. 56 is a schematic illustration of an equivalent circuit of a memoryarray in which a write “1” operation is being performed by impactionization according to an embodiment of the present invention.

FIG. 57 schematically illustrates a selected memory cell of the array ofFIG. 56 on which the write “1” operation is being performed, and thebias conditions thereon.

FIG. 58 schematically illustrates a link according to another embodimentof the present invention.

FIG. 59A schematically illustrates a top view of a memory cell of thememory array of FIG. 58.

FIG. 59B is a sectional view of the memory cell of FIG. 59A taken alongline I-I′ of FIG. 59A.

FIG. 59C is a sectional view of the memory cell of FIG. 59A taken alongline II-II′ of FIG. 59A.

FIG. 60 shows an equivalent circuit representation of a memory array oflinks, including the link of FIG. 58

FIG. 61 is a schematic illustration of an equivalent circuit of a memoryarray in which a read operation is being performed on a selected memorycell according to an embodiment of the present invention.

FIG. 62 schematically illustrates the selected memory cell of the arrayrepresented in FIG. 61 and bias conditions thereon during the readoperation.

FIG. 63 is a schematic illustration of an equivalent circuit of a memoryarray in which a write “0” operation is being performed according to anembodiment of the present invention.

FIG. 64 schematically illustrates a memory cell of the array representedin FIG. 63 that is having a write “0” operation performed thereonaccording to an embodiment of the present invention.

FIG. 65 is a schematic illustration of an equivalent circuit of a memoryarray in which a write “0” operation is being performed according to analternative embodiment of the present invention that allows forindividual bit writing.

FIG. 66 schematically illustrates a selected memory cell of the arrayrepresented in FIG. 65 that is being written to by the write “0”operation according to the alternative embodiment described with regardto FIG. 65.

FIG. 67 is a schematic illustration of an equivalent circuit of a memoryarray in which a write “1” operation is being performed by impactionization according to an embodiment of the present invention.

FIG. 68 schematically illustrates a selected memory cell of the array ofFIG. 67 on which the write “1” operation is being performed, and thebias conditions thereon.

FIG. 69 is a schematic illustration of an equivalent circuit of a memoryarray in which a write “1” operation is being performed by impactionization according to an embodiment of the present invention.

FIG. 70 schematically illustrates a selected memory cell of the array ofFIG. 69 on which the write “1” operation is being performed, and thebias conditions thereon.

FIG. 71 shows a memory array where adjacent regions are connected acommon BL terminal through a conductive region according to analternative embodiment of the present invention.

FIG. 72A shows a memory array according to another embodiment of thepresent invention.

FIG. 72B shows, in isolation, a memory cell from the memory array ofFIG. 72A.

FIGS. 72C and 72D show sectional views of the memory cell of FIG. 72Btaken along lines I-I′ and II-II′ of FIG. 72B, respectively.

FIG. 73 is an equivalent circuit representation of a memory array of thetype shown in FIG. 72A according to an embodiment of the presentinvention.

FIG. 74A shows an equivalent circuit representation of the memory cellof FIGS. 72B-72D according to an embodiment of the present invention.

FIG. 74B shows an energy band diagram of the intrinsic n-p-n bipolardevice of FIG. 74B when the floating body region is positively chargedand a positive bias voltage is applied to the buried well region,according to an embodiment of the present invention.

FIG. 74C shows an energy band diagram of the intrinsic n-p-n bipolardevice 30 of FIG. 74A when the floating body region is neutrally chargedand a bias voltage is applied to the buried well region, according to anembodiment of the present invention.

FIG. 75 is a schematic illustration of a memory array in which a readoperation is being performed on a selected memory cell according to anembodiment of the present invention.

FIG. 76 is a schematic illustration of the selected memory cell in FIG.75 that is being read, and bias conditions thereon during the readoperation.

FIG. 77 is a schematic illustration of a memory array in which a write“0” operation is being performed according to an embodiment of thepresent invention.

FIG. 78 schematically illustrates a memory cell of the array representedin FIG. 77 that is having a write “0” operation performed thereonaccording to an embodiment of the present invention.

FIG. 79 is a schematic illustration of a memory array in which a write“0” operation is being performed according to an alternative embodimentof the present invention.

FIG. 80 schematically illustrates a memory cell of the array representedin FIG. 79 that is having a write “0” operation performed thereonaccording to the alternative embodiment described with regard to FIG.79.

FIG. 81 is a schematic illustration of a memory array in which a write“1” operation is being performed by band-to-band tunneling according toan embodiment of the present invention.

FIG. 82 schematically illustrates a selected memory cell of the array ofFIG. 81 on which the write “1” operation is being performed, and thebias conditions thereon.

FIG. 83 is a schematic illustration of a memory array in which a write“1” operation is being performed by impact ionization according to anembodiment of the present invention.

FIG. 84 schematically illustrates a selected memory cell of the array ofFIG. 83 on which the write “1” operation is being performed, and thebias conditions thereon.

DETAILED DESCRIPTION OF THE INVENTION

Before the present devices cells, devices and methods are described, itis to be understood that this invention is not limited to particularembodiments described, as such may, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting, since the scope of the present invention will be limited onlyby the appended claims.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassedwithin the invention. The upper and lower limits of these smaller rangesmay independently be included or excluded in the range, and each rangewhere either, neither or both limits are included in the smaller rangesis also encompassed within the invention, subject to any specificallyexcluded limit in the stated range. Where the stated range includes oneor both of the limits, ranges excluding either or both of those includedlimits are also included in the invention.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, the preferred methodsand materials are now described. All publications mentioned herein areincorporated herein by reference to disclose and describe the methodsand/or materials in connection with which the publications are cited.

It must be noted that as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include plural referents unless thecontext clearly dictates otherwise. Thus, for example, reference to “acell” includes a plurality of such cells and reference to “the contact”includes reference to one or more contacts and equivalents thereof knownto those skilled in the art, and so forth.

The publications discussed herein are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the present invention isnot entitled to antedate such publication by virtue of prior invention.Further, the dates of publication provided may be different from theactual publication dates which may need to be independently confirmed.

Definitions

A “memory cell” as used herein, refers to a semiconductor memory cellcomprising an electrically floating body as the data storage element.

A “contactless memory cell” as used herein, refers to a memory cellwhich does not have a contact (or contacts) forming a directconnection(s) to a control line (or control lines). Contactless memorycells are typically connected in series when formed in a string or inparallel when formed in a link.

A “memory string” or “string” as used herein, refers to a set ofinterconnected memory cells connected in series, where conductiveregions at the surfaces of adjacent memory cells are shared orelectrically connected. In a series connection, the same current flowsthrough each of the memory cells.

A “link” as used herein, refers to a set of interconnected memory cellsconnected in parallel, where conductive regions at the surfaces ofadjacent memory cells are electrically connected. In a parallelconnection, the voltage drop across each of the memory cells is thesame.

A “memory array” or “memory cell array” as used herein, refers to aplurality of memory cells typically arranged in rows and columns. Theplurality of memory cells may further be connected in strings or linkswithin the memory array.

A “holding operation”, “standby operation” or “holding/standbyoperation”, as used herein, refers to a process of sustaining a state ofa memory cell by maintaining the stored charge.

A “multi-level write operation” refers to a process that includes anability to write more than two different states into a memory cell tostore more than one bit per cell.

A “write-then-verify” “write and verify” or “alternating write andverify” algorithm or operation refers to a process where alternatingwrite and read operations to a memory cell are employed to verifywhether a desired memory state of the memory cell has been achievedduring the write operation.

DESCRIPTION

Referring now to FIG. 1, a memory cell 50 according to an embodiment ofthe present invention is shown. The cell 50 is fabricated on asilicon-on-insulator (SOI) substrate 12 having a first conductivity type(such as p-type conductivity), which consists of buried oxide (BOX)layer 22.

A first region 16 having a second conductivity type, such as n-type, forexample, is provided in substrate 12 and is exposed at surface 14. Asecond region 18 having the second conductivity type is also provided insubstrate 12, and is also exposed at surface 14. Additionally, secondregion 18 is spaced apart from the first region 16 as shown in FIG. 1.First and second regions 16 and 18 may be formed by an implantationprocess formed on the material making up substrate 12, according to anyof implantation processes known and typically used in the art.Alternatively, a solid state diffusion process can be used to form firstand second regions 16 and 18.

A floating body region 24 having a first conductivity type, such asp-type conductivity type, is bounded by surface 14, first and secondregions 16, 18, buried oxide layer 22, and substrate 12. The floatingbody region 24 can be formed by an implantation process formed on thematerial making up substrate 12, or can be grown epitaxially. A gate 60is positioned in between the regions 16 and 18, and above the surface14. The gate 60 is insulated from surface 14 by an insulating layer 62.Insulating layer 62 may be made of silicon oxide and/or other dielectricmaterials, including high-K dielectric materials, such as, but notlimited to, tantalum peroxide, titanium oxide, zirconium oxide, hafniumoxide, and/or aluminum oxide. The gate 60 may be made of polysiliconmaterial or metal gate electrode, such as tungsten, tantalum, titaniumand their nitrides.

Cell 50 further includes word line (WL) terminal 70 electricallyconnected to gate 60, source line (SL) terminal 72 electricallyconnected to region 16, bit line (BL) terminal 74 electrically connectedto region 18, and substrate terminal 78 electrically connected tosubstrate 12 at a location beneath insulator 22. A memory array 80having a plurality of memory cells 50 is schematically illustrated inFIG. 2A.

The operation of a memory cell has been described (and also describesthe operation of memory cell 50) for example in “A Capacitor-less1T-DRAM Cell”, S. Okhonin et al., pp. 85-87, IEEE Electron DeviceLetters, vol. 23, no. 2, February 2002, which is hereby incorporatedherein, in its entirety, by reference thereto. The memory cell statesare represented by the charge in the floating body 24. If cell 50 hasholes stored in the floating body region 24, then the memory cell 50will have a lower threshold voltage (gate voltage where transistor isturned on) compared to when cell 50 does not store holes in floatingbody region 24.

The charge stored in the floating body 24 can be sensed by monitoringthe cell current of the memory cell 50. If cell 50 is in a state “1”having holes in the floating body region 24, then the memory cell willhave a lower threshold voltage (gate voltage where the transistor isturned on), and consequently a higher cell current (e.g. current flowingfrom BL to SL terminals), compared to if cell 50 is in a state “0”having no holes in floating body region 24. A sensing circuit/readcircuitry 90 typically connected to BL terminal 74 of memory array 80(e.g., see read circuitry 90 in FIG. 2B) can then be used to determinethe data state of the memory cell. Examples of such read operations aredescribed in Yoshida et al., “A Design of a Capacitorless 1T-DRAM CellUsing Gate-Induced Drain Leakage (GIDL) Current for Low-power andHigh-speed Embedded Memory”, pp. 913-918, International Electron DevicesMeeting, 2003 and U.S. Pat. No. 7,301,803 “Bipolar reading technique fora memory cell having an electrically floating body transistor”, both ofwhich are hereby incorporated herein, in their entireties, by referencethereto. An example of a sensing circuit is described in Oshawa et al.,“An 18.5 ns 128 Mb SOI DRAM with a Floating body Cell”, pp. 458-459,609, IEEE International Solid-State Circuits Conference, 2005, which ishereby incorporated herein, in its entirety, by reference thereto.

A read operation can be performed by applying the following biasconditions: a positive voltage is applied to the selected BL terminal74, and a positive voltage greater than the positive voltage applied tothe selected BL terminal 74 is applied to the selected WL terminal 70,zero voltage is applied to the selected SL terminal 72, and zero voltageis applied to the substrate terminal 78. The unselected BL terminalswill remain at zero voltage, the unselected WL terminals will remain atzero or negative voltage, and the unselected SL terminals will remain atzero voltage.

In one particular non-limiting embodiment, about 0.0 volts is applied tothe selected SL terminal 72, about +0.4 volts is applied to the selectedterminal 74, about +1.2 volts is applied to the selected terminal 70,and about 0.0 volts is applied to substrate terminal 78. The unselectedterminals 74 remain at 0.0 volts, the unselected terminals 70 remain at0.0 volts, at the unselected SL terminals 72 remain at 0.0 volts. FIG. 3shows the bias conditions for the selected memory cell 50 a andunselected memory cells 50 b, 50 c, and 50 d in memory array 80. FIG. 4Aalso shows and example of bias conditions of the selected memory cell 50a. However, these voltage levels may vary.

The bias conditions on unselected memory cells during the exemplary readoperation described above with regard to FIG. 3 are shown in FIGS.4B-4D. The bias conditions for memory cells sharing the same row (e.g.memory cell 50 b) and those sharing the same column (e.g. memory cell 50c) as the selected memory cell 50 a are shown in FIG. 4B and FIG. 4C,respectively, while the bias condition for memory cells not sharing thesame row nor the same column as the selected memory cell 50 (e.g. memorycell 50 d) is shown in FIG. 4D.

For memory cells sharing the same row as the selected memory cell (e.g.memory cell 50 b), the WL terminal 70 is positively biased, but becausethe BL terminal 74 is grounded, there is no potential difference betweenthe BL and SL terminals and consequently these cells are turned off (seeFIG. 4B).

For memory cells sharing the same column as the selected memory cell(e.g. memory cell 50 c), a positive voltage is applied to the BLterminal 74. However, since zero or negative voltage is applied to theunselected WL terminal 70, these memory cells are also turned off (seeFIG. 4C).

For memory cells 50 not sharing the same row nor the same column as theselected memory cell (e.g. memory cell 50 d), both WL and BL terminalsare grounded. As a result, these memory cells are turned off (see FIG.4D).

An exemplary write “0” operation of the cell 50 is now described withreference to FIG. 5. A negative bias is applied to SL terminal 72, zeroor negative potential is applied to WL terminal 70, zero voltage isapplied to BL terminal 74 and zero voltage is applied to substrateterminal 78. The unselected SL terminal 72 remains grounded. Under theseconditions, the p-n junction between floating body 24 and region 16 ofthe selected cell 50 is forward-biased, evacuating any holes from thefloating body 24. In one particular non-limiting embodiment, about −1.2volts is applied to terminal 72, about 0.0 volts is applied to terminal70, and about 0.0 volts is applied to terminal 74 and 78. However, thesevoltage levels may vary, while maintaining the relative relationshipbetween the applied bias, as described above.

An example of bias conditions of the selected and unselected memorycells 50 during a write “0” operation is illustrated in FIGS. 6A-6B.Because a write “0” operation only involves a negative voltage appliedto the selected SL terminal 72, the bias conditions for all theunselected cells are the same. As can be seen, the unselected memorycells will be in a holding operation, with the BL terminal at about 0.0volts, WL terminal at zero or negative voltage, and the unselected SLterminal at about 0.0 volts.

Alternatively, a write “0” operation can be performed by applying anegative bias to the BL terminal 74 as opposed to the SL terminal 72.The SL terminal 72 will be grounded, while zero voltage is applied tothe substrate terminal 78, and zero or negative voltage is applied tothe WL terminal 70. Under these conditions, all memory cells sharing thesame BL terminal 74 will be written into state “0” as shown in FIG. 7.

The write “0” operation referred to above with regard to FIGS. 5-7 has adrawback in that all memory cells 50 sharing either the same SL terminal72 or the same BL terminal 74 will be written to simultaneously and as aresult, does not allow individual bit writing, i.e. writing to a singlecell 50 memory bit. To write multiple data to different memory cells 50,write “0” is first performed on all the memory cells, followed by write“1” operations on a selected bit or selected bits.

An alternative write “0” operation that allows for individual bitwriting can be performed by applying a positive voltage to WL terminal70, a negative voltage to BL terminal 74, zero or positive voltage to SLterminal 72, and zero voltage to substrate terminal 78. Under theseconditions, the floating body 24 potential will increase throughcapacitive coupling from the positive voltage applied to the WL terminal70. As a result of the floating body 24 potential increase and thenegative voltage applied to the BL terminal 74, the p-n junction between24 and region 18 is forward-biased, evacuating any holes from thefloating body 24. To reduce undesired write “0” disturb to other memorycells 50 in the memory array 80, the applied potential can be optimizedas follows: if the floating body 24 potential of state “1” is referredto V_(FB1), then the voltage applied to the WL terminal 70 is configuredto increase the floating body 24 potential by V_(FB1)/2 while −V_(FB1)/2is applied to BL terminal 74.

In one particular non-limiting embodiment, the following bias conditionsare applied to the selected memory cell 50 a: a potential of about 0.0volts to SL terminal 72, a potential of about −0.2 volts to BL terminal74, a potential of about +0.5 volts is applied to terminal 70, and about0.0 volts is applied to substrate terminal 78; while about 0.0 volts isapplied to unselected SL terminal 72, about 0.0 volts is applied tounselected BL terminal 74, about 0.0 volts is applied to unselected WLterminal 70, and about 0.0 volts is applied to unselected terminal 78.FIG. 8 shows the bias conditions in the above-described example, for theselected and unselected memory cells in memory array 80. However, thesevoltage levels may vary.

The bias conditions of the selected memory cell 50 a under the write “0”operation described with regard to FIG. 8 are further elaborated andshown in FIG. 9A. As described, the potential difference betweenfloating body 24 and region 18 (connected to BL terminal 74) is shown inFIG. 9A as having increased, resulting in a forward bias current whichevacuates holes from the floating body 24.

Examples of bias conditions on the unselected memory cells 50 duringwrite “0” operations described with regard to FIG. 8 are shown in FIGS.9B-9D. The bias conditions for memory cells sharing the same row (e.g.memory cell 50 b) are illustrated in FIG. 9B, and the bias conditionsfor memory cells sharing the same column (e.g. memory cell 50 c) as theselected memory cell 50 a are shown in FIG. 9C, while the biasconditions for memory cells not sharing the same row nor the same column(e.g. memory cell 50 d) as the selected memory cell 50 a are shown inFIG. 9D.

The floating body 24 potential of memory cells sharing the same row asthe selected memory cell (see FIG. 9B) will increase by ΔV_(FB) due tocapacitive coupling from WL terminal 70. For memory cells in state “0”,the increase in the floating body 24 potential is not sustainable as theforward bias current of the p-n diodes formed by floating body 24 andjunctions 16 and 18 will evacuate holes from floating body 24. As aresult, the floating body 24 potential will return to the initial state“0” equilibrium potential. For memory cells in state “1”, the floatingbody 24 potential will initially also increase by ΔV_(FB), which willresult in holes being evacuated from floating body 24. After thepositive bias on the WL terminal 70 is removed, the floating body 24potential will decrease by ΔV_(FB). If the initial floating body 24potential of state “1” is referred to as V_(FB1), the floating body 24potential after the write “0” operation will become V_(FB1)−ΔV_(FB).Therefore, the WL potential needs to be optimized such that the decreasein floating body potential of memory cells 50 in state “1” is not toolarge. For example, the maximum floating body potential due to thecoupling from the WL potential cannot exceed V_(FB1)/2.

For memory cells sharing the same column as the selected memory cell, anegative voltage is applied to the BL terminal 74 (see FIG. 9C),resulting in an increase in the potential difference between floatingbody 24 and region 18 connected to the BL terminal 74. As a result, thep-n diode formed between floating body 24 and junction 18 will beforward biased. For memory cells in state “0”, the increase in thefloating body 24 potential will not change the initial state “0” asthere is initially no hole stored in the floating body 24. For memorycells in state “1”, the net effect is that the floating body 24potential after write “0” operation will be reduced. Therefore, the BLpotential also needs to be optimized such that the decrease in floatingbody potential of memory cells 50 in state “1” is not too large. Forexample, a potential of −V_(FB1)/2 can be applied to the BL terminal 74.

As to memory cells not sharing the same row nor the same column as theselected memory cell, zero voltage is applied to the SL terminal 72,zero voltage is applied to the BL terminal 74, and zero or negativevoltage is applied to WL terminal 70, and zero voltage is applied tosubstrate terminal 78 (see FIG. 9D). As a result, holes will not beevacuated from floating body region 24.

A write “1” operation can be performed on memory cell 50 through impactionization as described, for example, in “A New 1T DRAM Cell withEnhanced Floating Body Effect”, Lin and Chang, pp. 23-27, IEEEInternational Workshop on Memory Technology, Design, and Testing, 2006,which was incorporated by reference above, or band-to-band tunnelingmechanism, as described for example in “A Design of a Capacitorless1T-DRAM Cell Using Gate-Induced Drain Leakage (GIDL) Current forLow-power and High-speed Embedded Memory”, Yoshida et al., pp. 913-918,International Electron Devices Meeting, 2003, which was incorporated byreference above.

An example of the bias conditions of the selected memory cell 50 under awrite “1” operation using band-to-band tunneling is illustrated in FIGS.10 and 11A. The negative bias applied to the WL terminal 70 and thepositive bias applied to the BL terminal 74 results in electrontunneling which results in electron flow to the BL terminal 74,generating holes which subsequently are injected to the floating body 24of the selected memory cell 50. The SL terminal 72 and the substrateterminal 78 are grounded during the write “1” operation.

In one particular non-limiting embodiment, the following bias conditionsare applied to the selected memory cell 50 a: a potential of about 0.0volts is applied to SL terminal 72, a potential of about +1.2 volts isapplied to BL terminal 74, a potential of about −1.2 volts is applied toWL terminal 70, and about 0.0 volts is applied to substrate terminal 78;while the following bias conditions are applied to the unselectedterminals: about 0.0 volts is applied to SL terminal 72, about 0.0 voltsis applied to BL terminal 74, a potential of about 0.0 volts is appliedto WL terminal 70, and about 0.0 volts is applied to substrate terminal78. FIG. 10 shows the bias conditions for the selected and unselectedmemory cells in memory array 80. However, these voltage levels may vary.

Examples of bias conditions of the unselected memory cells during write“1” operations of the type described above with regard to FIG. 10 areshown in FIGS. 11B-11D. The bias conditions for memory cells sharing thesame row (e.g. memory cell 50 b) are shown in FIG. 11B and the biasconditions for memory cells sharing the same column as the selectedmemory cell 50 a (e.g. memory cell 50 c) are shown in FIG. 11C. The biasconditions for memory cells 50 not sharing the same row nor the samecolumn as the selected memory cell 50 a (e.g. memory cell 50 d) areshown in FIG. 11D.

For memory cells sharing the same row as the selected memory cell, bothterminals 72 and 74 are grounded, while about −1.2 volts is applied toWL terminal 70 (see FIG. 11B). There is no hole injection into thefloating body 24 of memory cell 50 b as there is not enough potentialdifference for band-to-band tunneling to occur.

For memory cells sharing the same column as the selected memory cell, apositive voltage is applied to the BL terminal 74 (see FIG. 11C). Nohole injection will occur for these memory cells as the WL terminal 70is being grounded.

For memory cells 50 not sharing the same row or the same column as theselected memory cell, both the SL terminal 72 and the BL terminal 74remain grounded (see FIG. 11D). Consequently, no write operations willoccur to these memory cells.

An example of the bias conditions of the selected memory cell 50 under awrite “1” operation using an impact ionization write “1” operation isillustrated in FIGS. 12 and 13A-13D. A positive bias is applied to theselected WL terminal 70, zero voltage is applied to all SL terminals 72,a positive bias applied to the selected BL terminal 74, while thesubstrate terminal 78 of the selected cell is grounded. These conditioncause hole injection to the floating body 24 of the selected memory cell(e.g. cell 50 a in FIG. 13A).

In one particular non-limiting embodiment, the following bias conditionsare applied to the selected memory cell 50 a: a potential of about 0.0volts is applied to SL terminal 72, a potential of about +1.2 volts isapplied to BL terminal 74, a potential of about +1.2 volts is applied tothe selected WL terminal 70, and about 0.0 volts is applied to substrateterminal 78; while the following bias conditions are applied to theunselected terminals: about 0.0 volts is applied to unselected SLterminal 72, about 0.0 volts is applied to unselected BL terminal 74, apotential of about 0.0 volts is applied to unselected WL terminal 70,and about 0.0 volts is applied to unselected substrate terminal 78. FIG.13A shows the bias conditions for the selected memory cell in theexample described above. FIG. 13B shows the bias conditions for memorycells sharing the same row as the selected memory cell in the exampledescribed above with regard to FIG. 12. FIG. 13C shows the biasconditions for memory cells sharing the same column as the selectedmemory cell in the example described above with regard to FIG. 12. FIG.13D shows the bias conditions for memory cells that share neither thesame row nor the same column as the selected memory cell in the exampledescribed above with regard to FIG. 12. However, these voltage levelsmay vary.

If floating body region 24 stores a positive charge, the positive chargestored will decrease over time due to the diode leakage current of thep-n junctions formed between the floating body 24 and regions 16 and 18,respectively, and due to charge recombination. A positive bias can beapplied to region 16 (connected to SL terminal 72) and/or to region 18(connected to BL terminal 74), while zero or negative voltage is appliedto WL terminal 70 and substrate terminal 78.

In one particular non-limiting embodiment, the following bias conditionsare applied to the selected memory cell 50: a potential of about +1.2volts is applied to SL terminal 72, a potential of about +1.2 volts isapplied to BL terminal 74, a potential of 0.0 volts is applied to WLterminal 70, and 0.0 volts is applied to substrate terminal 78. Underthese conditions, the p-n junctions formed between the floating body 24and regions 16 and 18 are reverse biased, improving the lifetime of thepositive charge stored in the floating body region 24.

The connection between region 16 of the memory cell 50 and the SLterminal 72 and the connection between region 18 of the memory cell 50and the BL terminal 74 are usually made through conductive contacts,which for example could be made of polysilicon or tungsten. FIG. 14shows contact 71 connecting region 16 and the SL terminal 72 and contact73 connecting region 18 and the BL terminal 74. Many difficulties arisewith contact formation. For example, separation between the contact andother electrodes (e.g. the gate electrode or neighboring contacts) mustbe provided to avoid electrical shorts between neighboring conductiveregions. Difficulties related to contact formation and some potentialsolutions are described for example in U.S. Patent ApplicationPublication No. 2010/0109064, titled “Semiconductor Device andManufacturing Method Thereof”, which is hereby incorporated herein, inits entirety, by reference thereto.

To simplify the manufacturing of the memory cell 50 and to reduce thesize of the memory 50, adjacent memory cells can be designed to share acommon region 16 (and SL terminal 72) or a common region 18 (and BLterminal 74). For example, as shown in FIG. 15, U.S. Pat. No. 6,937,516,“Semiconductor Device” to Fazan and Okhonin, which is herebyincorporated herein, in its entirety, by reference thereto, shows anarrangement where adjacent memory cells share common contacts 50 and 52.This reduces the number of contacts from two contacts per memory cell(when adjacent contacts are not shared between adjacent memory cells) towhere the number of contacts of memory cells in connection equals thenumber of memory cells plus one. For example, in FIG. 15, the number ofinterconnected memory cells (the cross section shows memory cellsinterconnected in the same column) is four and the number of contacts isfive.

The present invention provides a semiconductor memory device having aplurality of floating body memory cells which are connected either inseries to from a string, or in parallel to form a link. The connectionsbetween the memory cells are made to reduce the number of contacts foreach memory cell. In some embodiments, connections between controllines, such as source line or bit line, to the memory cells are made atthe end or ends of a string or link of several memory cells, such thatmemory cells not at the end are “contactless” memory cells, because nocontacts are provided on these cells to connect them to control lines.Rather, they are in direct contact with other memory cells that they areimmediately adjacent to. Because several memory cells are connectedeither in series or in parallel, a compact memory cell can be achieved.

FIG. 16A shows a cross-sectional schematic illustration of a memorystring 500 that includes a plurality of memory cells 50 (50 a-50 n inFIG. 16A, although there may be more or fewer cells 50), while FIG. 16Bshows a top view of the memory cell array 80, which shows two strings500 of memory cells 50 between the SL terminal 72 and BL terminal 74.Each memory string 500 includes a plurality of memory cells 50 connectedin a NAND architecture, in which the plurality of memory cells 50 areserially connected to make one string of memory cells. In a seriesconnection, the same current flows through each of the memory cells 50,from the BL terminal 74 to the SL terminal 72, or vice versa. String 500includes “n” memory cells 50, where “n” is a positive integer, whichtypically ranges between eight and sixty-four (although this numbercould be lower than eight (as low as two) or higher than sixty-four),and in at least one example, is sixteen. The region 18 of a secondconductivity at one end of the memory string is connected to the BLterminal 74, while the source region 16 of a second conductivity at theother end of the memory string is connected to the SL terminal 72.Although FIG. 16B schematically illustrates an array of two strings, itshould be noted that the present invention is not limited to twostrings.

Each memory cell transistor 50 includes a floating body region 24 of afirst conducting type, and first and second regions 20 (corresponding tofirst and second regions 16 and 18 in the single cell embodiments ofcell 50 described above) of a second conductivity type, which are spacedapart from each other and define a channel region. A buried insulatorlayer 22 isolates the floating body region 24 from the bulk substrate12. A gate 60 is positioned above the surface of floating body 24 and isin between the first and second regions 20. An insulating layer 62 isprovided between gate 60 and floating body 24 to insulate gate 60 fromfloating body 24. As can be seen in FIGS. 16A-16B, connections to thecontrol lines SL terminal 72 and BL terminal 74 are only made at theends of the string 500. Connection between SL terminal 72 and region 16is made through contact 71 and connection between BL terminal 74 andregion 18 is made through contact 73. No contact are made to the regions20 of the memory cells 50 in memory string 500, resulting in contactlessmemory cells intermediate of the end memory cells. In some embodiments,the transistors at the end of the string 500 (e.g., cells 50 a and 50 nin FIG. 16A) may be configured as access transistors to the memorystring 500, wherein the charges stored in the associated floating bodies24 (in the FIG. 16A example, 24 a and 24 n) are not read.

FIG. 17 shows an equivalent circuit representation of the memory array80 of FIG. 16B. In FIG. 17, the memory cells are arranged in a grid,with the rows of the memory array being defined by the WL terminals 70,while the columns are defined by the BL terminals 74. Within eachcolumn, multiple memory cells 50 are serially connected forming thestring 500. Adjacent columns are separated by columns of isolation 26(see FIG. 16B), such as shallow trench isolation (STI).

A read operation is described with reference to FIGS. 18 and 19A-19B.The read operation can be performed by applying the following biasconditions, where memory cell 50 c is being selected in this example: apositive voltage is applied to the selected BL terminal 74, and apositive voltage greater than the positive voltage applied to theselected BL terminal 74 is applied to the selected WL terminal 70, zerovoltage is applied to the selected SL terminal 72, and zero voltage isapplied to the substrate terminal 78. The unselected BL terminals 74will remain at zero voltage and the unselected SL terminals 72 willremain at zero voltage. A positive voltage greater than the positivevoltage applied to the selected WL terminal 70 c is applied to passingWL terminals 70 a, 70 b, 701, 70 m, and 70 n (see FIGS. 18 and 19A-19B).Passing WL terminals are connected to the gates of the passing cells,i.e. the unselected cells which are serially connected to the selectedmemory cell 50 c (e.g. memory cells 50 a, 50 b, 501, 50 m, and 50 n inFIG. 18). The voltages applied to the gate of the passing cells are suchthat the passing transistors are turned on, irrespective of thepotentials of their floating body regions. The passing cells need to beturned on because in a series connection, the current flows from the BLterminal 74 to SL terminal 72 (or vice versa) thereby flowing througheach of the memory cells 50. As a result, the passing cells will passthe potentials applied to the SL terminal 72 and BL terminal 74 to thesource and drain regions 20 b and 20 c of the selected cell 50 c. Forexample, the memory cell 50 n will pass the voltage applied to the BLterminal 74 to region 20 m connected to cell 50 n (and 50 m), whichmemory cell 50 m will subsequently pass to the region 201 connected tocell 501. The adjacent passing memory cells will subsequently pass thevoltage applied to BL terminal 74 until the voltage reaches region 20 cof the selected cell 50 c.

In one particular non-limiting embodiment, the following bias conditionsare applied to the selected memory cell 50 c: a potential of about 0.0volts is applied to SL terminal 72, a potential of about +0.4 volts isapplied to BL terminal 74, a potential of about +1.2 volts is applied toselected WL terminal 70, about +3.0 volts is applied to passing WLterminals 70, and about 0.0 volts is applied to substrate terminal 78;while the following bias conditions are applied to the unselectedterminals: about 0.0 volts is applied to SL terminal 72 (i.e.,unselected SL terminal 72 not shown in FIG. 19A), about 0.0 volts isapplied to BL terminal 74, a potential of about 0.0 volts is applied toWL terminal 70 that are not passing WL terminals (not shown in FIG.19A), and about 0.0 volts is applied to substrate terminal 78. FIGS. 18and 19A-19B show bias condition for the selected and unselected memorycells in memory array 80. However, these voltage levels may vary.

Under these conditions, about +1.2 volts will be applied to the gate 60of the selected cell 50 c and about 0.0 volts and 0.4 volts will bepassed to the regions 20 b and 20 c of the selected cells 50 c, similarto the read condition described in FIG. 4A. As described, the passingcells are biased so that its channels are conducting, and therefore thecurrent flowing from the BL terminal 74 and SL terminal 72 of the string500 is then determined by the potential of the floating body region 24of the selected cell 50 c. If cell 50 c is in a state “1” having holesin the floating body region 24, then the memory cell will have a lowerthreshold voltage (gate voltage where the transistor is turned on), andconsequently be conducting a larger current compared to if cell 50 c isin a state “0” having no holes in floating body region 24.

A sensing circuit/read circuitry 90 typically connected to BL terminal74 of memory array 80 (e.g., see read circuitry 90 in FIG. 19B) can beused to determine the data state of the memory cell. An example of asensing circuit is described in Ohsawa et al., “An 18.5 ns 128 Mb SOIDRAM with a Floating body Cell”, pp. 458-459, 609, IEEE InternationalSolid-State Circuits Conference, 2005, which is hereby incorporatedherein, in its entirety, by reference thereto.

A write “0” operation is described with reference to FIGS. 20-21. Biasconditions shown include: zero voltage applied to the SL terminal 72,zero voltage applied to the WL terminals 70, and negative voltageapplied to the BL terminal 74, while the substrate terminal 78 isgrounded. Under these conditions, the p-n junctions between floatingbodies 24 and regions 20 of the respective memory cells in string 500are forward-biased, evacuating any holes from each floating body 24. Inone particular non-limiting embodiment, about −1.2 volts is applied toterminal 74, about 0.0 volts is applied to terminal 70, about 0.0 voltsis applied to terminal 72 and about 0.0 volts is applied to terminal 78.Alternatively, a positive voltage can be applied to the WL terminals 70to ensure that the negative voltage applied to the BL terminal 74 ispassed to all the memory cells in string 500. However, these voltagelevels may vary, while maintaining the relative relationship between thecharges applied, as described above.

An alternative write “0” operation that allows for individual bitwriting is shown in FIGS. 22A-22B. This write “0” operation can beperformed by applying a negative voltage to BL terminal 74, zero voltageto SL terminal 72, zero voltage to substrate terminal 78, and a positivevoltage to passing WL terminals. The selected WL terminal is initiallygrounded until the voltages applied to SL terminal 72 and BL terminal 74reach the regions 20 b and 20 c, respectively, of the selected memorycell 50 c. Subsequently, the potential of the selected WL terminal 70(70 c in this example) is raised to a positive voltage higher than thepositive voltage applied to passing WL terminals. Under theseconditions, a positive voltage will be applied to the gate of theselected memory cell (e.g. memory cell 50 c in FIGS. 22A-22B) andconsequently the floating body 24 potential will increase throughcapacitive coupling from the positive voltage applied to the WL terminal70. The passing cells (e.g. memory cell 501, 50 m, and 50 n) will passthe negative voltage applied to the BL terminal 74 to the region 20 c ofthe memory cell 50 c, while passing cells 50 a and 50 b will pass zerovoltage applied to the SL terminal 72 to the region 20 b of the memorycell 50 c. Under these conditions, the bias conditions of the selectedmemory cell 50 c will be similar to the conditions described in FIG. 9A.As a result of the floating body 24 potential increase and the negativevoltage applied to the BL terminal 74, the p-n junction between 24 c andregion 20 c is forward-biased, evacuating any holes from the floatingbody 24. To reduce undesired write “0” disturb to other memory cells 50in the memory array 80, the applied potential can be optimized asfollows: if the floating body 24 potential of state “1” is referred toV_(FB1), then the voltage applied to the selected WL terminal 70 isconfigured to increase the floating body 24 potential by V_(FB1)/2 while−V_(FB1)/2 is applied to BL terminal 74. The voltage applied to WLterminal of the passing cells is optimized such that it is high enoughto pass the negative voltage applied to the BL terminal 74, but cannotbe too high to prevent the potential of the floating body 24 of thepassing cells becoming too high, which will result in holes beingevacuated from the passing cells that are in state “1”. A higherpositive voltage can be applied to passing WL terminals passing zerovoltage applied to the SL terminal 72 (e.g. passing WL terminals to theleft of selected WL terminal 70 c, i.e. 70 a and 70 b in FIG. 22A) thanthe voltage applied to passing WL terminals passing negative voltageapplied to the BL terminal 74 (e.g. passing WL terminals to the right ofselected WL terminal 70 c). This is because the higher voltage appliedto terminal 72 (compared to the negative voltage applied to terminal 74)may require a higher passing gate voltage for the passing transistors tobe turned on.

In one particular non-limiting embodiment, the following bias conditionsare applied to the memory string 500: a potential of about 0.0 volts isapplied to SL terminal 72, a potential of about −0.2 volts is applied toBL terminal 74, a potential of about +0.5 volts is applied to selectedterminal 70, a potential of about +0.2 volts is applied to passing WLterminals 70 and about 0.0 volts is applied to substrate terminal 78;while about 0.0 volts is applied to unselected SL terminal 72, about 0.0volts is applied to unselected BL terminal 74, about 0.0 volts isapplied to unselected (but not passing) WL terminal 70, and about 0.0volts is applied to unselected terminal 78. FIG. 22A shows the biasconditions for the selected and passing memory cells in selected memorystring 500, while FIG. 22B shows the bias conditions for selected andunselected memory cells in memory array 80 where memory cell 50 c is theselected cell. However, these voltage levels may vary.

Under these bias conditions, a positive voltage will be applied to thegate 60 of the selected cell 50 c, while a negative voltage applied tothe BL terminal 74 will be passed to the region 20 c of the selectedcell 50 c, and zero voltage applied to the SL terminal 72 will be passedto the region 20 b of the selected cell 50 c. This condition is similarto the condition described in FIG. 9A, which will result in holeevacuation out of the floating body 24 of the cell 50 c.

A write “1” operation can be performed on memory cell 50 through impactionization as described for example in Lin et al., “A New 1T DRAM Cellwith Enhanced Floating Body Effect”, pp. 23-27, IEEE InternationalWorkshop on Memory Technology, Design, and Testing, 2006, which wasincorporated by reference above, or by a band-to-band tunnelingmechanism, as described for example in Yoshida et al., “A Design of aCapacitorless 1T-DRAM Cell Using Gate-Induced Drain Leakage (GIDL)Current for Low-power and High-speed Embedded Memory”, pp. 913-918,International Electron Devices Meeting, 2003, which was incorporated byreference above.

An example of bias conditions of a selected memory cell 50 during aband-to-band tunneling write “1” operation is illustrated in FIGS. 23Aand 23B. A negative bias is applied to the selected WL terminal 70, apositive voltage is applied to the passing WL terminals 70, zero voltageis applied to the SL terminal 72 (and to all SL terminals 72), and apositive bias is applied to the selected BL terminal 74 (zero voltage isapplied to unselected BL terminals 74), while the substrate terminal 78is grounded. These conditions cause hole injection to the floating body24 of the selected memory cell (e.g. cell 50 c in FIGS. 23A-23B).

In one particular non-limiting embodiment, the following bias conditionsare applied to the selected memory string 500: a potential of about 0.0volts is applied to SL terminal 72, a potential of about +1.2 volts isapplied to BL terminal 74, a potential of about −1.2 volts is applied tothe selected WL terminal 70, about +3.0 volts is applied to the passingWL terminals 70, and about 0.0 volts is applied to substrate terminal78; while the following bias conditions are applied to the unselectedterminals: about 0.0 volts is applied to SL terminal 72, about 0.0 voltsis applied to BL terminal 74, a potential of about 0.0 volts is appliedto unselected (but not passing) WL terminal 70 (not shown in FIG. 23B),and about 0.0 volts is applied to substrate terminal 78. FIG. 23A showsthe bias conditions for the selected and passing memory cells inselected memory string 500, while FIG. 23B shows the bias conditions forthe selected and unselected memory cells in memory array 80, wherememory cell 50 c is the selected cell. However, these voltage levels mayvary.

Under these bias conditions, a negative voltage will be applied to thegate 60 of the selected cell 50 c, while a positive voltage applied tothe BL terminal 74 will be passed to the region 20 c of the selectedcell 50 c, and zero voltage applied to the SL terminal 72 will be passedto the region 20 b of the selected cell 50 c. This condition is similarto the condition described in FIG. 11A, which will result in holeinjection to the floating body 24 of the cell 50 c.

An example of the bias conditions of the selected memory cell 50 underan impact ionization write “1” operation is illustrated in FIGS.24A-24B. A positive bias is applied to the selected WL terminal 70, apositive voltage more positive than the positive voltage applied to theselected WL terminal 70 is applied to the passing WL terminals 70, zerovoltage is applied to the SL terminal 72 (both the selected SL terminal72 as well as all other SL terminals 72), and a positive bias is appliedto the selected BL terminal 74 (zero voltage is applied to theunselected BL terminals 74), while the substrate terminal 78 isgrounded. These conditions cause hole injection to the floating body 24of the selected memory cell (e.g. cell 50 c in FIGS. 24A-24B).

In one particular non-limiting embodiment, the following bias conditionsare applied to the selected memory string 500: a potential of about 0.0volts is applied to SL terminal 72, a potential of about +1.2 volts isapplied to BL terminal 74, a potential of about +1.2 volts is applied tothe selected WL terminal 70, about +3.0 volts is applied to the passingWL terminals 70, and about 0.0 volts is applied to substrate terminal78; while the following bias conditions are applied to the unselectedterminals (i.e., terminals in strings other than the string that theselected cell is in): about 0.0 volts is applied to SL terminal 72,about 0.0 volts is applied to BL terminal 74, a potential of about 0.0volts is applied to WL terminal 70 (not shown in FIG. 24B), and about0.0 volts is applied to substrate terminal 78. FIG. 24A shows the biasconditions for the selected and passing memory cells in selected memorystring 500, while FIG. 24B shows bias conditions for selected andunselected memory cells in memory array 80 (with memory cell 50 c as theselected cell). However, these voltage levels may vary.

A multi-level write operation can be performed using an alternatingwrite and verify algorithm, where a write pulse is first applied to thememory cell 50, followed by a read operation to verify if the desiredmemory state has been achieved. If the desired memory state has not beenachieved, another write pulse is applied to the memory cell 50, followedby another read verification operation. This loop is repeated until thedesired memory state is achieved.

For example, using band-to-band hot hole injection, a positive voltageis applied to BL terminal 74, zero voltage is applied to SL terminal 72,a negative voltage is applied to the selected WL terminal 70, a positivevoltage is applied to the passing WL terminals, and zero voltage isapplied to the substrate terminal 78. Positive voltages of differentamplitudes are applied to BL terminal 74 to write different states tofloating body 24. This results in different floating body potentials 24corresponding to the different positive voltages or the number ofpositive voltage pulses that have been applied to BL terminal 74. In oneparticular non-limiting embodiment, the write operation is performed byapplying the following bias conditions: a potential of about 0.0 voltsis applied to SL terminal 72, a potential of about −1.2 volts is appliedto the selected WL terminal 70, about +3.0 volts is applied to thepassing WL terminals, and about 0.0 volts is applied to substrateterminal 78, while the potential applied to BL terminal 74 isincrementally raised. For example, in one non-limiting embodiment, 25millivolts is initially applied to BL terminal 74, followed by a readverify operation. If the read verify operation indicates that the cellcurrent has reached the desired state (i.e. cell current correspondingto whichever state of states 00, 01, 10 or 11 is desired is achieved),then the multi write operation is concluded. If the desired state is notachieved, then the voltage applied to BL terminal 74 is raised, forexample, by another 25 millivolts, to 50 millivolts. This issubsequently followed by another read verify operation, and this processiterates until the desired state is achieved. However, the voltagelevels described may vary. The write operation is followed by a readoperation to verify the memory state.

The string 500 may be provided as planar cells, such as the embodimentsdescribed above with reference to FIGS. 1 and 16A, or may be provided asfin-type, three-dimensional cells, such as those illustrated in FIGS.25A-25B, for example. Other variations, modifications and alternativecells 50 may be provided without departing from the scope of the presentinvention and its functionality.

Referring now to FIG. 26, a memory cell 150 according to an embodimentof the present invention is shown. The cell 150 is fabricated on a bulksubstrate 12 having a first conductivity type (such as p-typeconductivity). A buried layer 22 of a second conductivity type (such asn-type conductivity) is also provided in the substrate 12 and buried inthe substrate 12, as shown. Buried layer 22 may be formed by an ionimplantation process on the material of substrate 12. Alternatively,buried layer 22 can be grown epitaxially.

A first region 16 having the second conductivity type is provided insubstrate 12 and first region 16 is exposed at surface 14. A secondregion 18 having the second conductivity type is also provided insubstrate 12, is also exposed at surface 14 and is spaced apart from thefirst region 16. First and second regions 16 and 18 may be formed by animplantation process formed on the material making up substrate 12,according to any of implantation processes known and typically used inthe art. Alternatively, a solid state diffusion process can be used toform first and second regions 16 and 18.

A floating body region 24 having a first conductivity type, such asp-type conductivity type, is bounded by surface 14, first and secondregions 16, 18, insulating layers 26, and buried layer 22. Insulatinglayers 26 (e.g., shallow trench isolation (STI)), may be made of siliconoxide, for example. Insulating layers 26 insulate cell 150 fromneighboring cells 150 when multiple cells 150 are joined in an array180. The floating body region 24 can be formed by an implantationprocess formed on the material making up substrate 12, or can be grownepitaxially. A gate 60 is positioned in between the regions 16 and 18,and above the surface 14. The gate 60 is insulated from surface 14 by aninsulating layer 62. Insulating layer 62 may be made of silicon oxideand/or other dielectric materials, including high-K dielectricmaterials, such as, but not limited to, tantalum peroxide, titaniumoxide, zirconium oxide, hafnium oxide, and/or aluminum oxide. The gate60 may be made of polysilicon material or metal gate electrode, such astungsten, tantalum, titanium and their nitrides.

Cell 150 further includes word line (WL) terminal 70 electricallyconnected to gate 60, source line (SL) terminal 72 electricallyconnected to region 16, bit line (BL) terminal 74 electrically connectedto region 18, buried well (BW) terminal 76 connected to buried layer 22,and substrate terminal 78 electrically connected to substrate 12 at alocation beneath insulator 22.

The operation of a memory cell 150 has been described for example inRanica et al., “Scaled 1T-Bulk Devices Built with CMOS 90 nm Technologyfor Low-cost eDRAM Applications”, pp. 38-41, Tech. Digest, Symposium onVLSI Technology, 2005 and application Ser. No. 12/797,334, titled“Method of Maintaining the State of Semiconductor Memory HavingElectrically Floating Body Transistor”, both of which are herebyincorporated herein, in their entireties, by reference thereto.

Memory cell states are represented by the charge in the floating body24. If cell 150 has holes stored in the floating body region 24, thenthe memory cell 150 will have a lower threshold voltage (gate voltagewhere transistor is turned on) compared to when cell 150 does not storeholes in floating body region 24.

As shown in FIG. 27A, inherent in this embodiment of the memory cell 150are n-p-n bipolar devices 130 a, 130 b formed by buried well region 22,floating body 24, and SL and BL regions 16, 18. A holding operation canbe performed by utilizing the properties of the n-p-n bipolar devices130 a, 130 b through the application of a positive back bias to the BWterminal 76 while grounding terminal 72 and/or terminal 74. If floatingbody 24 is positively charged (i.e. in a state “1”), the bipolartransistor 130 a formed by SL region 16, floating body 24, and buriedwell region 22 and bipolar transistor 130 b formed by BL region 18,floating body 24, and buried well region 22 will be turned on.

A fraction of the bipolar transistor current will then flow intofloating region 24 (usually referred to as the base current) andmaintain the state “1” data. The efficiency of the holding operation canbe enhanced by designing the bipolar devices 130 a, 130 b formed byburied well layer 22, floating region 24, and regions 16/18 to be alow-gain bipolar device, where the bipolar gain is defined as the ratioof the collector current flowing out of BW terminal 76 to the basecurrent flowing into the floating region 24.

For memory cells in state “0” data, the bipolar devices 130 a, 130 bwill not be turned on, and consequently no base hole current will flowinto floating region 24. Therefore, memory cells in state “0” willremain in state “0”.

An example of the bias conditions applied to cell 150 to carry out aholding operation includes: zero voltage is applied to BL terminal 74,zero voltage is applied to SL terminal 72, zero or negative voltage isapplied to WL terminal 70, a positive voltage is applied to the BWterminal 76, and zero voltage is applied to substrate terminal 78. Inone particular non-limiting embodiment, about 0.0 volts is applied toterminal 72, about 0.0 volts is applied to terminal 74, about 0.0 voltsis applied to terminal 70, about +1.2 volts is applied to terminal 76,and about 0.0 volts is applied to terminal 78. However, these voltagelevels may vary.

FIG. 27B shows an energy band diagram of the intrinsic n-p-n bipolardevice 130 when the floating body region 24 is positively charged and apositive bias voltage is applied to the buried well region 22. Thedashed lines indicate the Fermi levels in the various regions of then-p-n transistor 130. The Fermi levels are located in the band gapbetween the solid line 17 indicating the top of the valance band (thebottom of the band gap) and the solid line 19 indicating the bottom ofthe conduction band (the top of the band gap). The positive charge inthe floating body region 24 lowers the energy barrier of electron flowinto the floating body region 24 (i.e., the base region of the n-p-nbipolar device). Once injected into the floating body region 24, theelectrons will be swept into the buried well region 22 (connected to BWterminal 76) due to the positive bias applied to the buried well region22. As a result of the positive bias, the electrons are accelerated andcreate additional hot carriers (hot hole and hot electron pairs) throughan impact ionization mechanism. The resulting hot electrons flow intothe BW terminal 76 while the resulting hot holes will subsequently flowinto the floating body region 24. This process restores the charge onfloating body 24 to its maximum level and will maintain the chargestored in the floating body region 24 which will keep the n-p-n bipolartransistor 130 on for as long as a positive bias is applied to theburied well region 22 through BW terminal 76.

If floating body 24 is neutrally charged (the voltage on floating body24 being equal to the voltage on grounded bit line region 16), a statecorresponding to state “0”, the bipolar device will not be turned on,and consequently no base hole current will flow into floating region 24.Therefore, memory cells in the state “0” will remain in the state “0”.

FIG. 27C shows an energy band diagram of the intrinsic n-p-n bipolardevice 130 when the floating body region 24 is neutrally charged and abias voltage is applied to the buried well region 22. In this state theenergy level of the band gap bounded by solid lines 17A and 19A isdifferent in the various regions of n-p-n bipolar device 130. Becausethe potential of the floating body region 24 and the bit line region 16are equal, the Fermi levels are constant, resulting in an energy barrierbetween the bit line region 16 and the floating body region 24. Solidline 23 indicates, for reference purposes, the energy barrier betweenthe bit line region 16 and the floating body region 24. The energybarrier prevents electron flow from the bit line region 16 (connected toBL terminal 74) to the floating body region 24. Thus the n-p-n bipolardevice 130 will remain off.

Although the embodiment discussed in FIGS. 27A through 27C refers tobipolar devices 130 as n-p-n transistors, persons of ordinary skill inthe art will readily appreciate that by reversing the first and secondconnectivity types and inverting the relative values of the appliedvoltages memory cell 150 could include a bipolar device 130 which is ap-n-p transistor. Thus the choice of an n-p-n transistor as anillustrative example for simplicity of explanation in FIGS. 27A through27C is not limiting in any way. In addition, the discussions in regardto FIGS. 27A-27C use bipolar device 130 b formed by bit line region 18,floating body region 24, and buried well region 22, and the sameprinciples also apply to bipolar device 130 a formed by source lineregion 16, floating body region 24 and buried well region 22.

The charge stored in the floating body 24 can be sensed by monitoringthe cell current of the memory cell 150. If cell 150 is in a state “1”having holes in the floating body region 24, then the memory cell willhave a lower threshold voltage (gate voltage where the transistor isturned on), and consequently a higher cell current (e.g. current flowingfrom BL to SL terminals), compared to if cell 150 is in a state “0”having no holes in floating body region 24. Examples of the readoperation is described in Yoshida et al., “A Design of a Capacitorless1T-DRAM Cell Using Gate-Induced Drain Leakage (GIDL) Current forLow-power and High-speed Embedded Memory”, pp. 913-918, InternationalElectron Devices Meeting, 2003; Ohsawa et al., “An 18.5 ns 128 Mb SOIDRAM with a Floating body Cell”, pp. 458-459, 609, IEEE InternationalSolid-State Circuits Conference, 2005; and U.S. Pat. No. 7,301,803“Bipolar reading technique for a memory cell having an electricallyfloating body transistor”, which are hereby incorporated herein, intheir entireties, by reference thereto.

A read operation can be performed on cell 150 by applying the followingbias conditions: zero voltage is applied to the BW terminal 76, zerovoltage is applied to SL terminal 72, a positive voltage is applied tothe selected BL terminal 74, and a positive voltage greater than thepositive voltage applied to the selected BL terminal 74 is applied tothe selected WL terminal 70, while zero voltage is applied to substrateterminal 78. When cell 150 is in an array 180 of cells 150 (e.g., seeFIG. 28), the unselected BL terminals 74 will remain at zero voltage andthe unselected WL terminals 70 will remain at zero or negative voltage.In one particular non-limiting embodiment, about 0.0 volts is applied toterminal 72, about +0.4 volts is applied to the selected terminal 74 a,about +1.2 volts is applied to the selected terminal 70 a, about 0.0volts is applied to terminal 76, and about 0.0 volts is applied toterminal 78, as illustrated in FIG. 28.

A write “0” operation of the cell 150 is now described with reference toFIG. 29. In this example, to write “0” to cell 150, a negative bias isapplied to SL terminal 72, zero voltage is applied to BL terminal 74,zero or negative voltage is applied to WL terminal 70, zero or positivevoltage is applied to BW terminal 76, and zero voltage is applied tosubstrate terminal 78. The SL terminal 72 for the unselected cells 150that are not commonly connected to the selected cell 150 a will remaingrounded. Under these conditions, the p-n junctions (junction between 24and 16) are forward-biased, evacuating any holes from the floating body24. In one particular non-limiting embodiment, about −1.2 volts isapplied to terminal 72, about 0.0 volts is applied to terminal 74, about0.0 volts is applied to terminal 70, about 0.0 volts is applied toterminal 76, and about 0.0 volts is applied to terminal 78. However,these voltage levels may vary, while maintaining the relativerelationships between the charges applied, as described above. Underthese conditions, all memory cells sharing the same SL terminal 72 willbe written into state “0”.

A write “0” operation can also be performed by applying a negative biasto the BL terminal 74 as opposed to the SL terminal 72. The SL terminal72 will be grounded, while zero or positive voltage is applied to BWterminal 76, zero voltage is applied to the substrate terminal 78, andzero or negative voltage is applied to the WL terminal 70. Under theseconditions, all memory cells sharing the same BL terminal 74 will bewritten into state “0”.

The write “0” operations referred to above with regard to FIG. 29 have adrawback in that all memory cells 150 sharing either the same SLterminal 72 or the same BL terminal 74 will be written to simultaneouslyand as a result, these operations do not allow individual bit writing,i.e. writing to a single cell 150 memory bit. To write multiple data todifferent memory cells 150, write “0” is first performed on all thememory cells, followed by write “1” operations on a selected bit orselected bits.

An alternative write “0” operation, which, unlike the previous write “0”operations described above with regard to FIG. 29, allows for individualbit write, can be performed by applying a positive voltage to WLterminal 70, a negative voltage to BL terminal 74, zero or positivevoltage to SL terminal 72, zero or positive voltage to BW terminal 76,and zero voltage to substrate terminal 78, an example of which isillustrated in FIG. 30. Under these conditions, the floating body 24potential will increase through capacitive coupling from the positivevoltage applied to the WL terminal 70. As a result of the floating body24 potential increase and the negative voltage applied to the BLterminal 74, the p-n junction (junction between 24 and 18) isforward-biased, evacuating any holes from the floating body 24. Theapplied bias to selected WL terminal 70 and selected BL terminal 74 canpotentially affect the states of the unselected memory cells 150 sharingthe same WL or BL terminal as the selected memory cell 150. To reduceundesired write “0” disturb to other memory cells 150 in the memoryarray 180, the applied potential can be optimized as follows: if thefloating body 24 potential of state “1” is referred to as V_(FB1), thenthe voltage applied to the WL terminal 70 is configured to increase thefloating body 24 potential by V_(FB1)/2 while −V_(FB1)/2 is applied toBL terminal 74. This will minimize the floating body 24 potential changein the unselected cells 150 in state “1” sharing the same BL terminal asthe selected cell 150 from V_(FB1) to V_(FB1)/2. For memory cells 150 instate “0” sharing the same WL terminal as the selected cell 150, unlessthe increase in floating body 24 potential is sufficiently high (i.e.,at least V_(FB)/3, see below), then both n-p-n bipolar devices 130 a and130 b will not be turned on, or so that the base hold current is lowenough that it does not result in an increase of the floating body 24potential over the time during which the write operation is carried out(write operation time). It has been determined according to the presentinvention that a floating body 24 potential increase of V_(FB)/3 is lowenough to suppress the floating body 24 potential increase. A positivevoltage can be applied to SL terminal 72 to further reduce the undesiredwrite “0” disturb on other memory cells 150 in the memory array. Theunselected cells will remain at holding state, i.e. zero or negativevoltage applied to WL terminal 70 and zero voltage applied to BLterminal 74.

In one particular non-limiting embodiment, for the selected cell 150 apotential of about 0.0 volts is applied to terminal 72, a potential ofabout −0.2 volts is applied to terminal 74, a potential of about +0.5volts is applied to terminal 70, about 0.0 volts is applied to terminal76, and about 0.0 volts is applied to terminal 78. For the unselectedcells not sharing the same WL terminal or BL terminal with the selectedmemory cell 150, about 0.0 volts is applied to terminal 72, about 0.0volts is applied to terminal 74, about 0.0 volts is applied to terminal70, about 0.0 volts is applied to terminal 76, and about 0.0 volts isapplied to terminal 78. FIG. 30 shows the aforementioned bias conditionsfor the selected memory cell 150 and other cells 150 in the array 180.However, these voltage levels may vary.

A write “1” operation can be performed on memory cell 150 through impactionization as described for example in Lin et al., “A New 1T DRAM Cellwith Enhanced Floating Body Effect”, pp. 23-27, IEEE InternationalWorkshop on Memory Technology, Design, and Testing, 2006, which wasincorporated by reference above, or a band-to-band tunneling mechanism,as described for example in Yoshida et al., “A Design of a Capacitorless1T-DRAM Cell Using Gate-Induced Drain Leakage (GIDL) Current forLow-power and High-speed Embedded Memory”, pp. 913-918, InternationalElectron Devices Meeting, 2003, which was incorporated by referenceabove.

An example of the bias conditions of the selected memory cell 150 undera band-to-band tunneling write “1” operation is illustrated in FIG. 31A.The negative bias applied to the WL terminal 70 (70 a in FIG. 31A) andthe positive bias applied to the BL terminal 74 (74 a in FIG. 31A)results in hole injection to the floating body 24 of the selected memorycell 150 (150 a in FIG. 31A). The SL terminal 72 (72 a in FIG. 31A) andthe substrate terminal 78 (78 a in FIG. 31A) are grounded during thewrite “1” operation, while zero or positive voltage can be applied to BWterminal 76 (76 a in FIG. 31A) (positive voltage can be applied tomaintain the resulting positive charge on the floating body 24 asdiscussed in the holding operation above). The unselected WL terminals70 (70 n in FIG. 31A) and unselected BL terminals 74 (74 n in FIG. 31A)will remain grounded.

In one particular non-limiting embodiment, the following bias conditionsare applied to the selected memory cell 150 a: a potential of about 0.0volts is applied to SL terminal 72, a potential of about +1.2 volts isapplied to BL terminal 74, a potential of about −1.2 volts is applied toWL terminal 70, about 0.0 volts is applied to BW terminal 76, and about0.0 volts is applied to substrate terminal 78; while the following biasconditions are applied to the unselected terminals: about 0.0 volts isapplied to SL terminal 72, about 0.0 volts is applied to BL terminal 74,a potential of about 0.0 volts is applied to WL terminal 70, about 0.0volts is applied to BW terminal 76 (or +1.2 volts so that unselectedcells are in the holding operation) and about 0.0 volts is applied tosubstrate terminal 78. FIG. 31A shows the bias condition for theselected memory cell 150. However, these voltage levels may vary.

FIG. 31B shows bias conditions of the selected (150 a) and unselected(150 b, 150 c, 150 d) memory cells 150 during an impact ionization write“1” operation. A positive voltage is applied to the selected WL terminal70 (i.e., 70 a in FIG. 31B) and a positive voltage is applied to theselected BL terminal 74 (i.e., 74 a in FIG. 31B), with the SL terminal72 (i.e., 72 a in FIG. 31B), the BW terminal 76 (i.e., 76 a in FIG.31B), and the substrate terminal 78 (i.e., 78 a in FIG. 31B) aregrounded. This condition results in a lateral electric field in thechannel region sufficient to create hot electrons, which subsequentlycreate electron and hole pairs, with the holes being subsequentlyinjected to the floating body region 24 of the selected memory cell. Theunselected WL terminals 70 and unselected BL terminals 74 are grounded,while the unselected BW terminal can be grounded or a positive voltagecan be applied thereto to maintain the states of the unselected cells.

In one particular non-limiting embodiment, the following bias conditionsare applied to the selected memory cell 150 a: a potential of about 0.0volts is applied to SL terminal 72, a potential of about +1.2 volts isapplied to BL terminal 74, a potential of about +1.2 volts is applied toWL terminal 70, about 0.0 volts is applied to BW terminal 76, and about0.0 volts is applied to substrate terminal 78; while the following biasconditions are applied to the unselected terminals: about 0.0 volts isapplied to SL terminal 72, about 0.0 volts is applied to BL terminal 74,a potential of about 0.0 volts is applied to WL terminal 70, about 0.0volts is applied to BW terminal 76 (or +1.2 volts so that unselectedcells are in the holding operation) and about 0.0 volts is applied tosubstrate terminal 78. FIG. 31B shows the bias conditions for theselected memory cell 150. However, these voltage levels may vary.

FIG. 32A shows a cross-sectional schematic illustration of a memorystring 520 that includes a plurality of memory cells 150 connected inseries, while FIG. 32B shows a top view of a memory cell array 180,which shows two strings of memory cells 520 between the SL terminal 72and BL terminal 74.

Although FIG. 32B schematically illustrates an array of two strings, itshould be noted that the present invention is not limited to twostrings, as one string, or more than two string can be made in the samemanner as described. Each memory string 520 includes a plurality ofmemory cells 150 connected in a NAND architecture, in which theplurality of memory cells 150 are serially connected to make one stringof memory cells. In a series connection, the same current flows througheach of the memory cells 150, from the BL terminal 74 to the SL terminal72, or vice versa. String 520 includes “n” memory cells 150, where “n”is a positive integer, which typically ranges between 8 and 64, and inat least one example, is 16. However, string 520 could have less thaneight cells (as low as two) or greater than sixty-four cells. The region18 of a second conductivity at one end of the memory string is connectedto the BL terminal 74, while the source region 16 of a secondconductivity at the other end of the memory string is connected to theSL terminal 72.

Each memory cell transistor 150 includes a floating body region 24 of afirst conducting type, and first and second regions 20 (corresponding tofirst and second regions 16 and 18 in the single cell embodiments ofcell 150 described above) of a second conductivity type, which arespaced apart from each other and define a channel region. Regions 20 ofadjacent memory cells within a string 520 are connected together by theconducting region 64.

A buried layer 22 isolates the floating body region 24 from the bulksubstrate 12, while insulating layers 26 isolate the floating bodyregion 24 between adjacent memory cells 150. A gate 60 is positionedabove the surface of floating body 24 and is in between the first andsecond regions 20. An insulating layer 62 is provided between gate 60and floating body 24 to insulate gate 60 from floating body 24.

FIG. 32C shows an equivalent circuit representation of a memory array180 that includes strings 520 a and 520 b as well as additional strings.In FIG. 32C, the memory cells are arranged in a grid, with the rows ofthe memory array 180 being defined by the WL terminals 70, while thecolumns are defined by the BL terminals 74. Within each column, multiplememory cells 150 are serially connected forming the string 520. Adjacentcolumns are separated by columns of isolation, such as shallow trenchisolation (STI).

The memory cell operations of memory string 520 will be described asfollows. As will be seen, the operation principles of this embodiment ofthe memory string 520 will follow the operation principles of memorystring 500 described above, where the back bias terminal 76 available inmemory string 520 can be used to perform holding operation. In someembodiments, the transistors at the end of the string 520 (e.g., cells150 a and 150 n in FIG. 32A) may be configured as access transistors tothe memory string 520, wherein the charges stored in the associatedfloating bodies 24 (floating bodies 24 a and 24 n in the example of FIG.32A) are not read.

A read operation is described with reference to FIGS. 33, 34A and 34B.The read operation can be performed by applying the following biasconditions, where memory cell 150 c within the memory string 520 a isbeing selected (as shown in FIG. 33): a positive voltage is applied tothe selected BL terminal 74, and a positive voltage greater than thepositive voltage applied to the selected BL terminal 74 is applied tothe selected WL terminal 70, zero voltage is applied to the selected SLterminal 72, zero or positive voltage is applied to BW terminal 76, andzero voltage is applied to the substrate terminal 78. The unselected BLterminals 74 will remain at zero voltage and the unselected SL terminals72 will remain at zero voltage as shown in FIG. 34A. A positive voltagegreater than the positive voltage applied to the selected WL terminal 70c is applied to passing WL terminals 70 a, 70 b, 701, 70 m, and 70 n(see FIGS. 33 and 34A-34B). Passing WL terminals are connected to thegates of the passing cells, i.e. the unselected cells which are seriallyconnected to the selected memory cell 150 c (e.g. memory cells 150 a,150 b, 1501, 150 m, and 150 n in FIG. 33). The voltages applied to thegates of the passing cells are such that the passing transistors areturned on, irrespective of the potentials of their floating bodyregions. The passing cells need to be turned on because in a seriesconnection, the current flows from the BL terminal 74 to the SL terminal72 (or vice versa) wherein current flows through each of the memorycells 150. As a result, the passing cells will pass the potentialsapplied to the SL terminal 72 and BL terminal 74 to the source and drainregions 20 b and 20 c of the selected cell 150 c. For example, thememory cell 150 n will pass the voltage applied to the BL terminal 74 toregion 20 m connected to cell 150 n (and 150 m), which memory cell 150 mwill subsequently pass to the region 201 connected to cell 1501, etc.The adjacent passing memory cells sequentially pass the voltage appliedto BL terminal 74 until it reaches region 20 c of the selected memorycell 50 c.

In one particular non-limiting embodiment, the following bias conditionsare applied to the selected memory cell 150: a potential of about 0.0volts is applied to SL terminal 72, a potential of about +0.4 volts isapplied to BL terminal 74, a potential of about +1.2 volts is applied toselected WL terminal 70, about +3.0 volts is applied to passing WLterminals 70, about 0.0 volts is applied to BW terminal 76, and about0.0 volts is applied to substrate terminal 78; while the following biasconditions are applied to the unselected terminals: about 0.0 volts isapplied to SL terminal 72, about 0.0 volts is applied to BL terminal 74,a potential of about 0.0 volts is applied to WL terminal 70 (but notpassing WL terminal), about 0.0 volts is applied to BW terminal 76 (or+1.2 volts is applied to BW terminal 76 to maintain the states of theunselected memory cells), and about 0.0 volts is applied to substrateterminal 78. FIGS. 34A-34B show the bias conditions for the selected andunselected memory cells in memory array 180. However, these voltagelevels may vary.

Under these conditions, about +1.2 volts will be applied to the gate 60c and about 0.0 volts and 0.4 volts will be passed to the regions 20 band 20 c of the selected cell 150 c, similar to the read conditiondescribed in FIG. 28. As described, the passing cells are biased so thattheir channels are conducting, and therefore the current flowing fromthe BL terminal 74 and SL terminal 72 of the string 520 is thendetermined by the potential of the floating body region 24 of theselected cell 150 c. If cell 150 c is in a state “1” having holes in thefloating body region 24, then the memory cell will have a lowerthreshold voltage (gate voltage where the transistor is turned on), andconsequently be conducting a larger current compared to if cell 150 isin a state “0” having no holes in floating body region 24.

The current flow from the BL terminal 74 to SL terminal 72 can then bemeasured or sensed using a read circuitry 90 attached to BL terminal 74as illustrated in FIG. 34B. The memory state can then be determined bycomparing it with a reference value generated by a reference generatorcircuitry 92 coupled to a reference cell in memory string 520R as shownin FIG. 34B.

A write “0” operation is described with reference to FIGS. 35-36, wherethe following bias conditions are applied: zero voltage to the SLterminal 72, zero voltage to the WL terminals 70, and negative voltageto the BL terminal 74, while the BW terminal 76 and substrate terminal78 are grounded. Under these conditions, the p-n junctions betweenfloating body 24 and regions 20 of the memory cells in string 520 areforward-biased, evacuating any holes from the floating bodies 24. In oneparticular non-limiting embodiment, about −1.2 volts is applied toterminal 74, about 0.0 volts is applied to terminal 70, and about 0.0volts is applied to terminals 72, 76, and 78. A positive voltage canalso be applied to the WL terminals 70 to ensure that the negativevoltage applied to the BL terminal 74 is passed to all the memory cellsin string 520. However, these voltage levels may vary, while maintainingthe relative relationships between the charges applied, as describedabove.

An alternative write “0” operation that allows for individual bitwriting is illustrated in FIGS. 37-38 and can be performed by applying anegative voltage to BL terminal 74, zero voltage to SL terminal 72, zerovoltage to BW terminal 76, zero voltage to substrate terminal 78, and apositive voltage to passing WL terminals. The selected WL terminal isinitially grounded until the voltages applied to SL terminal 72 and BLterminal 74 reach the regions 20 b and 20 c, respectively, of selectedmemory cell 150 c. Subsequently, the potential of the selected WLterminal 70 is raised to a positive voltage higher than the positivevoltage applied to passing WL terminals. Under these conditions, apositive voltage will be applied to the gate of the selected memory cell(e.g. memory cell 150 c in FIGS. 37-38) and consequently the floatingbody 24 potential will increase through capacitive coupling from thepositive voltage applied to the WL terminal 70. The passing cells (e.g.memory cell 1501, 150 m, and 150 n) will pass the negative voltageapplied to the BL terminal 74 to the region 20 c of the memory cell 150c, while passing cells 150 a and 150 b will pass zero voltage applied tothe SL terminal 72 to the region 20 b of the memory cell 150 c, similarto the conditions described in regard to FIG. 30. As a result of thefloating body 24 potential increase and the negative voltage applied tothe BL terminal 74, the p-n junction between floating body region 24 cand region 20 c is forward-biased, evacuating any holes from thefloating body 24. To reduce undesired write “0” disturb to other memorycells 150 in the memory array 180, the applied potential can beoptimized as follows: if the floating body 24 potential of state “1” isreferred to V_(FB1), then the voltage applied to the selected WLterminal 70 is configured to increase the floating body 24 potential byV_(FB1)/2 while −V_(FB1)/2 is applied to BL terminal 74. The voltageapplied to WL terminal of the passing cells is optimized such that it ishigh enough to pass the negative voltage applied to the BL terminal 74,but cannot be too high to prevent the potential of the floating body 24of the passing cells becoming too high, which will result in holes beingevacuated from the passing cells that are in state “1”. A higherpositive voltage can be applied to passing WL terminals passing zerovoltage applied to the SL terminal 72 (e.g. passing WL terminals to theleft of selected WL terminal 70 c, i.e. 70 a and 70 b in FIG. 37) thanthe voltage applied to passing WL terminals passing negative voltageapplied to the BL terminal 74 (e.g. passing WL terminals to the right ofselected WL terminal 70 c). This is because the higher voltage appliedto terminal 72 (compared to the negative voltage applied to terminal 74)may require a higher passing gate voltage for the passing transistors tobe turned on.

In one particular non-limiting embodiment, the following bias conditionsare applied to the memory string 520: a potential of about 0.0 volts toSL terminal 72, a potential of about −0.2 volts to BL terminal 74, apotential of about +0.5 volts is applied to selected terminal 70, apotential of about +0.2 volts is applied to passing WL terminals 70,about 0.0 volts is applied to BW terminal 76, and about 0.0 volts isapplied to substrate terminal 78; while about 0.0 volts is applied tounselected SL terminal 72, about 0.0 volts is applied to unselected BLterminal 74, about 0.0 volts is applied to BW terminal 76 (or +1.2 voltsis applied to BW terminal 76 to maintain the states of the unselectedmemory cells), about 0.0 volts is applied to unselected (but notpassing) WL terminal 70, and about 0.0 volts is applied to unselectedterminal 78. FIGS. 37-38 show the bias conditions for the selected andunselected memory cells in memory array 180 where memory cell 150 c isthe selected cell. However, these voltage levels may vary.

Under these bias conditions, a positive voltage will be applied to thegate 60 of the selected cell 150 c, while a negative voltage applied tothe BL terminal 74 will be passed to the region 20 c of the selectedcell 150 c, and zero voltage applied to the SL terminal 72 will bepassed to the region 20 b of the selected cell 150 c. This condition issimilar to the condition described in regard to FIG. 30, and results inhole evacuation out of the floating body 24 c of the cell 150 c.

A write “1” operation can be performed on memory cell 150 through impactionization as described for example in Lin et al., “A New 1T DRAM Cellwith Enhanced Floating Body Effect”, pp. 23-27, IEEE InternationalWorkshop on Memory Technology, Design, and Testing, 2006, which wasincorporated by reference above, or a write “1” operation can beperformed through a band-to-band tunneling mechanism, as described forexample in Yoshida et al., “A Design of a Capacitorless 1T-DRAM CellUsing Gate-Induced Drain Leakage (GIDL) Current for Low-power andHigh-speed Embedded Memory”, pp. 913-918, International Electron DevicesMeeting, 2003, which was incorporated by reference above.

An example of bias conditions on a selected memory cell 150 under aband-to-band tunneling write “1” operation is illustrated in FIGS. 39and 40. A negative bias is applied to the selected WL terminal 70, apositive voltage is applied to the passing WL terminals 70, zero voltageis applied to the SL terminal 72, and a positive bias applied to the BLterminal 74, zero voltage is applied to the BW terminal 76, while thesubstrate terminal 78 is grounded. This condition results in holeinjection to the floating body 24 of the selected memory cell (e.g. cell150 c in FIGS. 39-40).

In one particular non-limiting embodiment, the following bias conditionsare applied to the selected memory cell 150 c: a potential of about 0.0volts is applied to SL terminal 72, a potential of about +1.2 volts isapplied to BL terminal 74, a potential of about −1.2 volts is applied tothe selected WL terminal 70, about +3.0 volts is applied to the passingWL terminals 70, about 0.0 volts is applied to BW terminal 76, and about0.0 volts is applied to substrate terminal 78; while the following biasconditions are applied to the unselected terminals: about 0.0 volts isapplied to SL terminal 72, about 0.0 volts is applied to BL terminal 74,a potential of about 0.0 volts is applied to WL terminal 70 (but notpassing WL terminal), about 0.0 volts is applied to BW terminal 76 (or+1.2 volts is applied to maintain the states of the unselected memorycells), and about 0.0 volts is applied to substrate terminal 78. FIG. 40shows the bias conditions for the selected and unselected memory cellsin memory array 180 where memory cell 150 c is the selected cell.However, these voltage levels may vary.

Under these bias conditions, a negative voltage will be applied to thegate 60 of the selected cell 150 c, while a positive voltage applied tothe BL terminal 74 will be passed to the region 20 c of the selectedcell 150 c, and zero voltage applied to the SL terminal 72 will bepassed to the region 20 b of the selected cell 150 c. This condition issimilar to the condition described in FIG. 31A, and results in holeinjection to the floating body 24 c of the cell 150 c.

An example of the bias conditions on the selected memory cell 150 underan impact ionization write “1” operation is illustrated in FIGS. 41-42.A positive bias is applied to the selected WL terminal 70, a positivevoltage more positive than the positive voltage applied to the selectedWL terminal 70 is applied to the passing WL terminals 70, zero voltageis applied to the SL terminal 72, a positive bias is applied to the BLterminal 74, and zero voltage is applied to BW terminal 76, while thesubstrate terminal 78 is grounded. These conditions result in holeinjection to the floating body 24 of the selected memory cell (e.g. cell150 c in FIGS. 41-42).

In one particular non-limiting embodiment, the following bias conditionsare applied to the selected memory cell 150 c: a potential of about 0.0volts is applied to SL terminal 72, a potential of about +1.2 volts isapplied to BL terminal 74, a potential of about +1.2 volts is applied tothe selected WL terminal 70, about +3.0 volts is applied to the passingWL terminals 70, about 0.0 volts is applied to BW terminal 76, and about0.0 volts is applied to substrate terminal 78; while the following biasconditions are applied to the unselected terminals: about 0.0 volts isapplied to SL terminal 72, about 0.0 volts is applied to BL terminal 74,a potential of about 0.0 volts is applied to WL terminal 70 (but notpassing WL terminal), about 0.0 volts is applied to BW terminal 76 (or+1.2 volts is applied to BW terminal 76 to maintain the states of theunselected memory cells), and about 0.0 volts is applied to substrateterminal 78. FIG. 42 shows the bias conditions for the selected andunselected memory cells in memory array 180 (with memory cell 150 c asthe selected cell). However, these voltage levels may vary.

A multi-level write operation can be performed using an alternatingwrite and verify algorithm, where a write pulse is first applied to thememory cell 150, followed by a read operation to verify if the desiredmemory state has been achieved. If the desired memory state has not beenachieved, another write pulse is applied to the memory cell 150,followed by another read verification operation. This loop is repeateduntil the desired memory state is achieved.

For example, using band-to-band hot hole injection, a positive voltageis applied to BL terminal 74, zero voltage is applied to SL terminal 72,a negative voltage is applied to the selected WL terminal 70, a positivevoltage is applied to the passing WL terminals, zero voltage is appliedto the BW terminal 76 and zero voltage is applied to the substrateterminal 78. Positive voltages of different amplitudes are applied to BLterminal 74 to write different states to floating body 24. This resultsin different floating body potentials 24 corresponding to the differentpositive voltages or the number of positive voltage pulses that havebeen applied to BL terminal 74. In one particular non-limitingembodiment, the write operation is performed by applying the followingbias conditions: a potential of about 0.0 volts is applied to SLterminal 72, a potential of about −1.2 volts is applied to the selectedWL terminal 70, about +3.0 volts is applied to the passing WL terminals,about 0.0 volts is applied to BW terminal 76, and about 0.0 volts isapplied to substrate terminal 78, while the potential applied to BLterminal 74 is incrementally raised. For example, in one non-limitingembodiment, 25 millivolts is initially applied to BL terminal 74,followed by a read verify operation. If the read verify operationindicates that the cell current has reached the desired state (i.e. cellcurrent corresponding to whichever state of 00, 01, 10 or 11 is thedesired state has been achieved), then the multi write operation isconcluded. If the desired state has not been not achieved, then thevoltage applied to BL terminal 74 is raised, for example, by another 25millivolts, to 50 millivolts. This is subsequently followed by anotherread verify operation, and this process iterates until the desired stateis achieved. However, the voltage levels described may vary. The writeoperation is followed by a read operation to verify the memory state.

The string 520 may be constructed from a plurality of planar cells, suchas the embodiments described above with reference to FIGS. 26 and 32A,or may be constructed from fin-type, three-dimensional cells, such asillustrated in FIGS. 43-44. Other variations, modifications andalternative cells 150 may be provided without departing from the scopeof the present invention and its functionality.

Another embodiment of memory array 280 is described with reference toFIGS. 45A-45B, where FIG. 45A shows a top view of the memory array 280consisting of two strings of memory cells 540 between the SL terminal 72and BL terminal 74, and FIG. 45B shows the cross section of a memorystring 540. Although FIG. 45A schematically illustrates an array of twostrings, it should be noted that the present invention is not limited totwo strings, as more than two, or even only one string could beprovided.

Each memory string 540 of array 280 includes a plurality of memory cells250 connected in a NAND architecture, in which the plurality of memorycells 250 are serially connected to make one string of memory cells.String 540 includes “n” memory cells 250, where “n” is a positiveinteger, which typically ranges between 8 and 64, and in at least oneexample, is 16. However, this embodiment, like the embodiment above isnot limited to the stated range, as fewer than eight or more thansixty-four cells could be included in a string. The region 18 of asecond conductivity at one end of the memory string is connected to theBL terminal 74 through contact 73, while the source region 16 of asecond conductivity at the other end of the memory string is connectedto the SL terminal 72 through contact 71. In some embodiments, thetransistors at the ends of the string 540 (e.g., cells 250 a and 250 nin the example of FIG. 45B) may be configured as access transistors tothe memory string 540, and charged stored in the associated floatingbodies 24 (24 a and 24 n in the example of FIG. 45B) are not read.

Referring to FIG. 45B, the memory cell 250 includes a substrate 12 of afirst conductivity type, such as p-type, for example. Substrate 12 istypically made of silicon, but may also comprise, for example,germanium, silicon germanium, gallium arsenide, carbon nanotubes, orother semiconductor materials. A buried layer 22 of a secondconductivity type such as n-type, for example, is provided in thesubstrate 12. Buried layer 22 may be formed by an ion implantationprocess on the material of substrate 12. Alternatively, buried layer 22can also be grown epitaxially on top of substrate 12.

A floating body region 24 of the first conductivity type, such asp-type, for example, is bounded on top by region 16 (or region 18 orregion 20) of the second conductivity type and insulating layer 62, onthe sides by region 16 (or region 18 or region 20) of the secondconductivity type and insulating layers 30 and 26 (like, for example,shallow trench isolation (STI)), may be made of silicon oxide, forexample. Insulating layer 30 and the region 16 (or region 18 or region20) of the second conductivity type insulate the floating body region 24along the I-I′ direction as shown in FIG. 45B, while insulating layer 28insulates the floating body region 24 along the II-II′ direction asshown in FIG. 45A.

Regions 16, 18, and 20 having a second conductivity type, such asn-type, for example, are provided in substrate 12 and are exposed atsurface 14. Regions 16, 18, and 20 may be formed by an implantationprocess formed on the material making up substrate 12, according to anyimplantation process known and typically used in the art. Alternatively,a solid state diffusion process could be used to form regions 16, 18,and 20. Although regions 16, 18, and 20 have the same conductivity type(for example n-type), the dopant concentration forming these regions canbe (but need not necessarily be) different. In FIGS. 45A and 45B,regions 16 and 18 are located at the ends of the memory string 540,while regions 20 are located inside the memory string 540, isolatingadjacent floating body regions 24 of adjacent memory cells 250.

A gate 60 is positioned above the surface of floating body 24 and is inbetween the first and second regions 20 (or between region 16 and region20 or between region 18 and region 20). The gate 60 is insulated fromfloating body region 24 by an insulating layer 62.

Insulating layer 62 may be made of silicon oxide and/or other dielectricmaterials, including high-K dielectric materials, such as, but notlimited to, tantalum peroxide, titanium oxide, zirconium oxide, hafniumoxide, and/or aluminum oxide. The gate 60 may be made of, for example,polysilicon material or metal gate electrode, such as tungsten,tantalum, titanium and their nitrides.

Memory string 540 further includes word line (WL) terminals 70electrically connected to gates 60, source line (SL) terminal 72electrically connected to region 16, bit line (BL) terminal 74electrically connected to region 18, buried layer (BW) terminal 76connected to buried layer 22, and substrate terminal 78 electricallyconnected to substrate 12.

The BW terminal 76 connected to the buried layer region 22 serves as aback bias terminal, i.e. a terminal at the back side of a semiconductortransistor device, usually at the opposite side of the gate of thetransistor.

A method of manufacturing memory array 280 will be described withreference to FIGS. 46A-46U. These figures are arranged in groups ofthree related views, with the first figure of each group being a topview of memory cell 250, the second figure of each group being avertical cross section of the top view in the first figure of the groupdesignated I-I′, and the third figure of each group being a verticalcross section of the top view in the first figure of the groupdesignated II-II′.

Turning now to FIGS. 46A through 46C, the first steps of the process canbe seen starting with growing a thick conductive region 202 comprised ofa different material from the materials forming the substrate region 12.The conductive region 202 can be selectively etched without removing thesubstrate region 12. For example, the conductive region 202 could bemade of silicon germanium (SiGe) material, while substrate 12 could bemade of silicon, although materials for both of these layers may vary.

As shown in FIGS. 46D through 46F, a pattern 30′ covering the areas tobecome insulator region 30 (as shown in the final structures in FIGS.46S through 46U) is formed using a lithography process. The conductiveregion 202 is then etched following the lithography pattern.

Referring to FIGS. 46G through 46I, a conductive region 204 comprisingfor example the same material forming the substrate 12 is grown (like,for example, silicon). A chemical mechanical polishing step can then beperformed to polish the resulting films so that the silicon surface isflat. Subsequently, a thin layer of silicon oxide 206 is grown on thesurface of film 204. This is followed by a deposition of a polysiliconlayer 208 and then silicon nitride layer 210.

Next, a pattern is formed for use in opening the areas to becomeinsulator regions 28. The pattern can be formed using a lithographyprocess. This is then followed by dry etching of the silicon nitridelayer 210, polysilicon layer 208, silicon oxide layer 206, and siliconlayer 204, creating trench 212, as shown in FIGS. 46J and 46L (trenches212 are not visible in the view of FIG. 46K).

A wet etch process that selectively removes the region 202 is thenperformed, leaving gaps that are mechanically supported by region 204The resulting gap regions are then oxidized to form buried oxide regions30 as shown in FIGS. 46N and 46O. Subsequently, the remaining siliconnitride layer 210, polysilicon layer 208, and silicon oxide layer 206are then removed, followed by a silicon oxide deposition process and achemical mechanical polishing step to planarize the resulting siliconoxide film, resulting in the silicon oxide insulator region 28 as shownin FIGS. 46M and 46O. Alternatively, the silicon deposition step can beperformed prior to the removal of the silicon nitride layer 210,polysilicon layer 208 and silicon oxide layer 206.

Referring to FIGS. 46P through 46R, an ion implantation step is nextperformed to form the buried layer region 22. Subsequently a siliconoxide layer (or high-dielectric material layer) 62 is formed on thesilicon surface (FIGS. 46Q-46R), followed by polysilicon (or metal)layer 214 deposition (FIGS. 46Q-46R).

A pattern covering the area to be made into gate 60 is next made, suchas by using a lithography process. The pattern forming step is followedby dry etching of the polysilicon (or metal) layer 214 and silicon oxide(or high dielectric materials) layer 62. An ion implantation step isthen performed to form the regions 20 of the second conductivity type(e.g. n-type). The conductive region 204 underneath the gate region 60is protected from the ion implantation process and is now bounded byregions 20, insulating layer 30 and insulating layer 28 on the sides,and by buried layer 22 from the substrate 12, and by insulating layer 62at the surface, forming the floating body region 24 (see FIG. 46T). Thisis then followed by backend process to form contact and metal layers(not shown in figures).

Another embodiment of memory array is shown as memory array 380 in FIG.47, wherein memory array 380 comprises a link connecting a plurality ofmemory cells 350 in parallel. FIG. 48A shows a top view of memory cell350 in isolation, with FIGS. 48B and 48C showing sectional views of thememory cell 350 taken along lines I-I′ and respectively.

Referring to FIGS. 48B and 48C together, the cell 350 is fabricated onsilicon on insulator (SOI) substrate 12 of a first conductivity typesuch as a p-type, for example. Substrate 12 is typically made ofsilicon, but may also comprise, for example, germanium, silicongermanium, gallium arsenide, carbon nanotubes, or other semiconductormaterials. A buried insulator layer 22, such as buried oxide (BOX), isprovided in the substrate 12.

A floating body region 24 of the first conductivity type, such asp-type, for example, is bounded on top by insulating layer 62, on thesides by regions 20 of a second conductivity type and insulating layers26, and on the bottom by buried layer 22. Insulating layers 26 (like,for example, shallow trench isolation (STI)), may be made of siliconoxide, for example. Insulating layers 26 insulate cell 350 fromneighboring cells 350 when multiple cells 350 are joined in an array 380to make a memory device as illustrated in FIGS. 47 and 49.

Regions 20 having a second conductivity type, such as n-type, forexample, are provided in substrate 12 and are exposed at surface 14.Regions 20 may be formed by an implantation process formed on thematerial making up substrate 12, according to any implantation processknown and typically used in the art. Alternatively, a solid statediffusion process could be used to form regions 20.

A gate 60 is positioned above the floating body region 24 and regions20. The gate 60 is insulated from floating body region 24 by aninsulating layer 62. Insulating layer 62 may be made of silicon oxideand/or other dielectric materials, including high-K dielectricmaterials, such as, but not limited to, tantalum peroxide, titaniumoxide, zirconium oxide, hafnium oxide, and/or aluminum oxide. The gate60 may be made of, for example, polysilicon material or metal gateelectrode, such as tungsten, tantalum, titanium and their nitrides.

Region 20 is continuous (electrically conductive) in the direction alongthe II-II′ direction (referring to FIG. 48A) and can be used to connectseveral memory cells 350 in parallel as shown in the equivalent circuitrepresentation of the memory array 380 in FIGS. 47 and 49 (where regions20 are connected to bet line (BL) terminals 74. Connections betweenregions 20 and bit line (BL) terminals 74 a and 74 b can be made throughcontacts 73 at the edge of the parallel connections (see FIG. 47). Anadjacent pair of continuous regions 20 can be used to connect a link ofcells 350 in parallel. Cell 350 further includes word line (WL) terminal70 electrically connected to gate 60 and substrate terminal 78electrically connected to substrate 12 (see FIGS. 48B-48C). In aparallel connection, the voltage applied to the BL terminals 74 is aboutthe same across all memory cells 350 (small differences might occur dueto voltage drop along the bit lines) and the current will only flowthrough the selected memory cell 350.

Because it is possible to minimize the number of connections to BLterminals by making them only at the edge of the parallel connections,the number of contacts can be reduced, for example to two contacts, foreach parallel connection. No contacts are made to the regions 20 of thememory cells 350 that are not at the edge of the parallel connections inmemory array 380, resulting in contactless memory cells in locationsthat are not at the edge (end). The number of contacts can be increasedto reduce the resistance of the parallel connections if desired.

A read operation is described with reference to FIGS. 50-51, wherememory cell 350 b is being selected (as shown in FIG. 50). The followingbias conditions may be applied: a positive voltage is applied to BLterminal 74 b, zero voltage is applied to BL terminal 74 c, a positivevoltage is applied to WL terminal 70 b, and zero voltage is applied tosubstrate terminal 78. The unselected BL terminals (e.g. BL terminal 74a, 74 d, . . . , 74 p in FIG. 50) are left floating, the unselected WLterminals (e.g. WL terminal 70 a, 70 m, 70 n in FIG. 50) will remain atzero voltage, and the unselected substrate terminal 78 will remain atzero voltage. Alternatively, the unselected BL terminals to the right ofBL terminal 74 c (where zero voltage is applied to) can be grounded. Apositive voltage of the same amplitude as that applied to BL terminal 74b can be applied to the unselected BL terminals to the left of BLterminal 74 b. Because the region 20 b (connected to BL terminal 74 b)is shared with the adjacent cell 350 a, the unselected BL terminals tothe left of BL terminal 74 b (where a positive voltage is applied to)need to be left floating or have a positive voltage applied thereto toprevent any parasitic current flowing from BL terminal 74 b to the BLterminals to the left of BL terminal 74 b. Alternatively, the biasconditions on BL terminals 74 b and 74 c (connected to regions 20 of theselected memory cell 350 b) may be reversed.

In one particular non-limiting embodiment, the following bias conditionsare applied to the selected memory cell 350 b: a potential of about +0.4volts is applied to BL terminal 74 b, a potential of about 0.0 volts isapplied to BL terminal 74 c, a potential of about +1.2 volts is appliedto WL terminal 70 b, and about 0.0 volts is applied to substrateterminal 78; while the following bias conditions are applied to theunselected terminals: about 0.0 volts is applied to unselected WLterminals, about 0.0 volts is applied to unselected substrate terminals,while the unselected BL terminals are left floating.

As shown in FIG. 51, about +1.2 volts are applied to the gate 60 b,about 0.4 volts are applied to the region 20 b (connected to BL terminal74 b), about 0.0 volts are applied to region 20 c (connected to BLterminal 74 c), and about 0.0 volts are applied to substrate 12 ofselected memory cell 350 b. The current flowing from BL terminal 74 b toBL terminal 74 c will then be determined by the potential of thefloating body region 24 of the selected cell 350 b.

If cell 350 b is in a state “1” having holes in the floating body region24, then the memory cell will have a lower threshold voltage (gatevoltage where the transistor is turned on), and consequently beconducting a larger current compared to if cell 350 b is in a state “0”having no holes in floating body region 24. The cell current can besensed by, for example, a sense amplifier circuit connected to BLterminal 74 b.

A write “0” operation is described with reference to FIGS. 52-53, wherethe following bias conditions are applied: zero voltage to the WLterminals 70, and negative voltage to the BL terminal 74 b, while thesubstrate terminal 78 is grounded. Under these conditions, the p-njunction between floating body 24 and region 20 b of the memory cell 350is forward-biased, evacuating any holes from the floating body 24. Theunselected BL terminals 74 can be left floating or grounded, theunselected WL terminals 70 will remain at zero voltage, and theunselected substrate terminal 78 will remain at zero voltage.

In one particular non-limiting embodiment, about −1.2 volts is appliedto terminal 74 b, about 0.0 volts is applied to terminal 70, and about0.0 volts is applied to terminal 78. However, these voltage levels mayvary, while maintaining the relative relationship between the chargesapplied, as described above. Because BL terminal 74 b is connected toseveral memory cells 350, all memory cells connected to BL terminal 74 bwill be written to state “0”, as indicated by the memory cells insidethe dashed lines in FIG. 52.

An alternative write “0” operation that allows for more selective bitwriting is shown in FIGS. 54-55 and can be performed by applying anegative voltage to BL terminal 74 b, zero voltage to substrate terminal78, and a positive voltage to WL terminal 70 b. The unselected WLterminals will remain at zero voltage, the unselected BL terminals willbe left floating or grounded, and the unselected substrate terminal 78will remain at zero voltage.

Under these conditions, a positive voltage will be applied to the gateof the selected memory cell (e.g. memory cell 350 a and 350 b in FIG.54, see also gate 60 b in FIG. 55) and consequently the floating body 24potential will increase through capacitive coupling from the positivevoltage applied to the WL terminal 70. As a result of the floating body24 potential increase and the negative voltage applied to the BLterminal 74 b, the p-n junction between 24 and region 20 b isforward-biased, evacuating any holes from the floating body 24. Toreduce undesired write “0” disturb to other memory cells 350 in thememory array 380, the applied potential can be optimized as follows: ifthe floating body 24 potential of state “1” is referred to V_(FB1), thenthe voltage applied to the selected WL terminal 70 is configured toincrease the floating body 24 potential by V_(FB1)/2 while −V_(FB1)/2 isapplied to BL terminal 74 b. Under these conditions, memory cell 350 aand 350 b will be written to state “0” (compared to the previous write“0” described above, which results in all memory cells sharing the sameBL terminal 74 b to be written to state “0”).

In one particular non-limiting embodiment, the following bias conditionsare applied to the memory cell 350: a potential of about −0.2 volts toBL terminal 74 b, a potential of about +0.5 volts is applied to selectedWL terminal 70 b, and about 0.0 volts is applied to substrate terminal78; while unselected BL terminals 74 are left floating, about 0.0 voltsis applied to unselected WL terminal 70, and about 0.0 volts is appliedto unselected terminal 78. FIGS. 54-55 show the bias conditions for theselected and unselected memory cells in memory array 380 where memorycells 350 a and 350 b are the selected cells. However, these voltagelevels may vary.

An example of the bias conditions on a selected memory cell 350 b underan impact ionization write “1” operation is illustrated in FIGS. 56-57.A positive bias is applied to the selected WL terminal 70 b, zerovoltage is applied to the BL terminal 74 c, a positive bias applied tothe BL terminal 74 b, while the substrate terminal 78 is grounded. Thiscondition results in a lateral electric field sufficient to generateenergetic electrons, which subsequently generate electron-hole pairs,followed by hole injection to the floating body 24 of the selectedmemory cell (e.g. cell 350 b in FIGS. 56-57). The unselected WLterminals (e.g. WL terminal 70 a, 70 c, 70 m, and 70 n in FIG. 56) aregrounded, the unselected BL terminals (e.g. BL terminal 74 a, 74 d, 74m, 74 n, 74 o, and 74 p in FIG. 56) are left floating, and theunselected substrate terminal 78 is grounded. Alternatively, theunselected BL terminals to the right of BL terminal 74 c (where zerovoltage is applied to) can be grounded. A positive voltage of the sameamplitude as that applied to BL terminal 74 b can be applied to theunselected BL terminals to the left of BL terminal 74 b. Because theregion 20 b (connected to BL terminal 74 b) is shared with the adjacentcell 350 a, the unselected BL terminals to the left of BL terminal 74 b(where a positive voltage is applied to) need to be left floating orapplied a positive voltage to prevent any parasitic current flowing fromBL terminal 74 b to the BL terminals to the left of BL terminal 74 b,which can cause undesired write “1” operations to at least oneunselected memory cell 350.

In one particular non-limiting embodiment, the following bias conditionsare applied to the selected memory cell 350 b: a potential of about 0.0volts is applied to BL terminal 74 c, a potential of about +1.2 volts isapplied to BL terminal 74 b, a potential of about +1.2 volts is appliedto the selected WL terminal 70 b, and about 0.0 volts is applied tosubstrate terminal 78; while the following bias conditions are appliedto the unselected terminals: a potential of about 0.0 volts is appliedto unselected WL terminals 70 (e.g. WL terminals 70 a, 70 m, and 70 n inFIG. 56), about 0.0 volts is applied to substrate terminal 78, and theunselected BL terminals 74 (e.g. BL terminals 74 c, 74 d, 74 m, 74 n, 74o, and 74 p in FIG. 56) are left floating. FIGS. 56-57 show the biasconditions for the selected and unselected memory cells in memory array380 (with memory cell 350 b as the selected cell). However, thesevoltage levels may vary.

Alternatively, the bias conditions on BL terminals 74 b and 74 c(connected to regions 20 of the selected memory cell 350 b) may bereversed.

FIG. 58 schematically illustrates a memory array according to anotherembodiment of the present invention. Memory array 480 includes aplurality of memory cells 450. FIG. 59A shows a top view of memory cell450 in isolation, with FIGS. 59B and 59C showing sectional views of thememory cell 450 taken along lines I-I′ and II-II′ of FIG. 58,respectively.

Referring to FIGS. 59B and 59C together, the cell 450 includes asubstrate 12 of a first conductivity type such as a p-type, for example.Substrate 12 is typically made of silicon, but may also comprise, forexample, germanium, silicon germanium, gallium arsenide, carbonnanotubes, or other semiconductor materials. A buried layer 22 of asecond conductivity type such as n-type, for example, is provided in thesubstrate 12. Buried layer 22 may be formed by an ion implantationprocess on the material of substrate 12. Alternatively, buried layer 22can be grown epitaxially on top of substrate 12.

A floating body region 24 of the first conductivity type, such asp-type, for example, is bounded on top by regions 20 and insulatinglayer 62, on the sides by insulating layers 26, and on the bottom byburied layer 22. Insulating layers 26 (like, for example, shallow trenchisolation (STI)), may be made of silicon oxide, for example. Insulatinglayers 26 insulate cell 450 from neighboring cells 450 when multiplecells 450 are joined in an array 480 to make a memory device asillustrated in FIG. 58.

Regions 20 having a second conductivity type, such as n-type, forexample, are provided in substrate 12 and are exposed at surface 14.Regions 20 are formed by an implantation process formed on the materialmaking up substrate 12, according to any implantation process known andtypically used in the art. Alternatively, a solid state diffusionprocess could be used to form regions 20.

A gate 60 is positioned above the floating body region 24, regions 20and insulating layers 26. The gate 60 is insulated from floating bodyregion 24 by an insulating layer 62. Insulating layer 62 may be made ofsilicon oxide and/or other dielectric materials, including high-Kdielectric materials, such as, but not limited to, tantalum peroxide,titanium oxide, zirconium oxide, hafnium oxide, and/or aluminum oxide.The gate 60 may be made of, for example, polysilicon material or metalgate electrode, such as tungsten, tantalum, titanium and their nitrides.

Region 20 is continuous (electrically conductive) in the direction alongthe II-II′ direction (referring to FIG. 59A) and can be used to connectseveral memory cells 450 in parallel as shown in the equivalent circuitrepresentation of the memory array 480 in FIGS. 58 and 60 (where theregions 20 are connected to bit line (BL) terminals 74). Connectionsbetween regions 20 and bit line (BL) terminals 74 a and 74 b can be madethrough contacts 73 at the edge of the parallel connections (see FIG.58). An adjacent pair of continuous regions 20 can be used to connect alink of cells 450 in parallel. In a parallel connection, the voltageapplied to the BL terminals 74 is about the same across all memory cells450 (small differences might occur due to voltage drop along the bitlines) and the current will only flow through the selected memory cell450. Cell 450 further includes word line (WL) terminal 70 electricallyconnected to gate 60, buried well (BW) terminal 76 connected to buriedlayer 22, and substrate terminal 78 electrically connected to substrate12 (se FIGS. 59B-59C).

Because it is possible to make connections to BL terminals only at theedge of the parallel connections, the number of contacts can be reduced,for example to two contacts, for each parallel connection. No contactsto the memory cells that are not at the edge of the parallel connectionare necessary, as these are contactless memory cells that arecontinuously linked by regions 20 The number of contacts can beincreased to reduce the resistance of the parallel connections ifdesired.

A read operation of the embodiment of FIGS. 58-59C is described withreference to FIGS. 61-62, where memory cell 450 b is being selected (asshown in FIG. 61). The following bias conditions may be applied: apositive voltage is applied to BL terminal 74 a, zero voltage is appliedto BL terminal 74 b, a positive voltage is applied to WL terminal 70 b,zero voltage is applied to BW terminal 76 and zero voltage is applied tosubstrate terminal 78. The unselected BL terminals (e.g. BL terminal 74c, 74 d, . . . , 74 p in FIG. 61) will remain at zero voltage, theunselected WL terminals (e.g. WL terminal 70 a, 70 m, 70 n in FIG. 61)will remain at zero voltage, the unselected BW terminals 76 will remainat zero voltage (or a positive bias can be applied to maintain thestates of the unselected memory cells), and the unselected substrateterminals 78 will remain at zero voltage. Alternatively, the biasconditions on BL terminals 74 a and 74 b (connected to regions 20 of theselected memory cell 450 b) may be reversed.

In one particular non-limiting embodiment, the following bias conditionsare applied to the selected memory cell 450 b: a potential of about +0.4volts is applied to BL terminal 74 a, a potential of about 0.0 volts isapplied to BL terminal 74 b, a potential of about +1.2 volts is appliedto WL terminal 70 b, about 0.0 volts is applied to BW terminal 76 andabout 0.0 volts is applied to substrate terminal 78; while the followingbias conditions are applied to the unselected terminals: about 0.0 voltsis applied to unselected BL terminals, about 0.0 volts is applied tounselected WL terminals, about 0.0 volts is applied to unselected BWterminals (or +1.2 volts is applied to BW terminal 76 to maintain thestates of the unselected memory cells), and about 0.0 volts is appliedto unselected substrate terminals.

As shown in FIG. 62, about +1.2 volts will be applied to the gate 60 b(connected to terminal 70 b), about 0.4 volts will be applied to theregion 20 a (connected to BL terminal 74 a), about 0.0 volts will beapplied to region 20 b (connected to BL terminal 74 b), about 0.0 voltswill be applied to buried layer 22, and about 0.0 will be applied tosubstrate 12 of selected memory cell 450 b. The current flowing from BLterminal 74 a to BL terminal 74 b will then be determined by thepotential of the floating body region 24 of the selected cell 450 b.

If cell 450 b is in a state “1” having holes in the floating body region24, then the memory cell will have a lower threshold voltage (gatevoltage where the transistor is turned on), and consequently beconducting a larger current compared to if cell 450 b is in a state “0”having no holes in floating body region 24. The cell current can besensed by, for example, a sense amplifier circuit connected to BLterminal 74 a.

A write “0” operation is described with reference to FIGS. 63-64, wherethe following bias conditions are applied: zero voltage to the BLterminal 74 b, zero voltage to the WL terminals 70, and negative voltageto the BL terminal 74 a, while the BW terminal 76 and substrate terminal78 are grounded. Under these conditions, the p-n junction betweenfloating body 24 and region 20 a of the memory cell 450 isforward-biased, evacuating any holes from the floating body 24. In oneparticular non-limiting embodiment, about −1.2 volts is applied toterminal 74 a, about 0.0 volts is applied to terminal 70, and about 0.0volts is applied to terminals 76 and 78. However, these voltage levelsmay vary, while maintaining the relative relationship between thecharges applied, as described above. Alternatively, the write “0”operation can be achieved by reversing the bias conditions applied to BLterminals 74 a and 74 b.

An alternative write “0” operation that allows for individual bitwriting are shown in FIGS. 65-66 and can be performed by applying anegative voltage to BL terminal 74 a, zero voltage to BL terminal 74 b,zero voltage to BW terminal 76, zero voltage to substrate terminal 78,and a positive voltage to WL terminal 70. Under these conditions, apositive voltage will be applied to the gate of the selected memory cell(e.g. memory cell 450 b in FIGS. 65-66) and consequently the floatingbody 24 potential will increase through capacitive coupling from thepositive voltage applied to the WL terminal 70. As a result of thefloating body 24 potential increase and the negative voltage applied tothe BL terminal 74 a, the p-n junction between 24 and region 20 a isforward-biased, evacuating any holes from the floating body 24. Toreduce undesired write “0” disturb to other memory cells 450 in thememory array 480, the applied potential can be optimized as follows: ifthe floating body 24 potential of state “1” is referred to V_(FB1), thenthe voltage applied to the selected WL terminal 70 is configured toincrease the floating body 24 potential by V_(FB1)/2 while −V_(FB1)/2 isapplied to BL terminal 74 a.

In one particular non-limiting embodiment, the following bias conditionsare applied to the memory cell 450 b: a potential of about 0.0 volts toBL terminal 74 b, a potential of about −0.2 volts to BL terminal 74 a, apotential of about +0.5 volts is applied to selected WL terminal 70 b,about 0.0 volts is applied to BW terminal 76, and about 0.0 volts isapplied to substrate terminal 78; while about 0.0 volts is applied tounselected BL terminals 74, about 0.0 volts is applied to BW terminal 76(or +1.2 volts is applied to BW terminal 76 to maintain the states ofthe unselected memory cells), about 0.0 volts is applied to unselectedWL terminal 70, and about 0.0 volts is applied to unselected terminal78. FIGS. 65-66 show the bias conditions for the selected and unselectedmemory cells in memory array 480 where memory cell 450 b is the selectedcell. However, these voltage levels may vary. Alternatively, the write“0” operation can be achieved by reversing the bias conditions appliedto BL terminals 74 a and 74 b.

An example of the bias conditions on a selected memory cell 450 bundergoing a band-to-band tunneling write “1” operation is illustratedin FIGS. 67 and 68. A negative bias is applied to the selected WLterminal 70 b, zero voltage is applied to the BL terminal 74 b, apositive bias is applied to the BL terminal 74 a, zero voltage isapplied to the BW terminal 76, and the substrate terminal 78 isgrounded. These conditions cause electrons flow to the BL terminal 74 a,generating holes which subsequently are injected into the floating bodyregion 24.

In one particular non-limiting embodiment, the following bias conditionsare applied to the selected memory cell 450 b: a potential of about 0.0volts is applied to BL terminal 74 b, a potential of about +1.2 volts isapplied to BL terminal 74 a, a potential of about −1.2 volts is appliedto the selected WL terminal 70 b, about 0.0 volts is applied to BWterminal 76, and about 0.0 volts is applied to substrate terminal 78;while the following bias conditions are applied to the unselectedterminals: about 0.0 volts is applied to unselected BL terminals (e.g.BL terminals 74 c, 74 d, 74 m, 74 n, 74 o, and 74 p in FIG. 67), apotential of about 0.0 volts is applied to unselected WL terminals 70(e.g. WL terminals 70 a, 70 m, and 70 n in FIG. 67), about 0.0 volts isapplied to unselected BW terminals 76 (or +1.2 volts is applied tomaintain the states of the unselected memory cells), and about 0.0 voltsis applied to unselected substrate terminals 78. FIGS. 67-68 show thebias conditions for the selected and unselected memory cells in memoryarray 480 where memory cell 450 b is the selected cell. However, thesevoltage levels may vary. Alternatively, the write “1” operation can beachieved by reversing the bias conditions applied to BL terminals 74 aand 74 b.

An example of the bias conditions on a selected memory cell 450 bundergoing an impact ionization write “1” operation is illustrated inFIGS. 69-70. A positive bias is applied to the selected WL terminal 70b, zero voltage is applied to the BL terminal 74 b, a positive bias isapplied to the BL terminal 74 a, zero voltage is applied to BW terminal76, and the substrate terminal 78 is grounded. These conditions cause alateral electric field sufficient to generate energetic electrons, whichsubsequently generate electron-hole pairs, followed by hole injectioninto the floating body 24 of the selected memory cell (e.g. cell 450 bin FIGS. 69-70).

In one particular non-limiting embodiment, the following bias conditionsare applied to the selected memory cell 450 b: a potential of about 0.0volts is applied to BL terminal 74 b, a potential of about +1.2 volts isapplied to BL terminal 74 a, a potential of about +1.2 volts is appliedto the selected WL terminal 70 b, about 0.0 volts is applied to BWterminal 76, and about 0.0 volts is applied to substrate terminal 78;while the following bias conditions are applied to the unselectedterminals: about 0.0 volts is applied to unselected BL terminals 74(e.g. BL terminals 74 c, 74 d, 74 m, 74 n, 74 o, and 74 p in FIG. 69), apotential of about 0.0 volts is applied to unselected WL terminals 70(e.g. WL terminals 70 a, 70 m, and 70 n in FIG. 69), about 0.0 volts isapplied to BW terminal 76 (or +1.2 volts is applied to BW terminal 76 tomaintain the states of the unselected memory cells), and about 0.0 voltsis applied to substrate terminal 78. FIGS. 69-70 show the biasconditions for the selected and unselected memory cells in memory array480 (with memory cell 450 b as the selected cell). However, thesevoltage levels may vary. Alternatively, the write “1” operation can beachieved by reversing the bias conditions applied to BL terminals 74 aand 74 b.

FIG. 71 shows an alternative embodiment of memory array 490, whereadjacent regions 20 are connected to a common BL terminal 74 through aconductive region 64. The operation of memory array 490 is similar tothat of memory array 380 fabricated on a silicon on insulator (SOI)surface, where regions 20 are shared between two adjacent memory cells350.

FIG. 72A shows another embodiment of a memory array, referred to as 580.Memory array 580 comprises a plurality of memory cells 550. FIG. 72Bshows a memory cell 550 in isolation while FIGS. 72C and 72D showsectional views of the memory cell 550 of FIG. 72B taken along linesI-I′ and II-II′ of FIG. 72B, respectively.

Memory cell 550 includes a substrate 12 of a first conductivity typesuch as a p-type, for example. Substrate 12 is typically made ofsilicon, but may also comprise, for example, germanium, silicongermanium, gallium arsenide, carbon nanotubes, or other semiconductormaterials. A buried layer 22 of a second conductivity type such asn-type, for example, is provided in the substrate 12. Buried layer 22may be formed by an ion implantation process on the material ofsubstrate 12. Alternatively, buried layer 22 can be grown epitaxially ontop of substrate 12.

A floating body region 24 of the first conductivity type, such asp-type, for example, is bounded on top by region 16 and insulating layer62, on the sides by insulating layers 26 and 28, and on the bottom byburied layer 22, see FIGS. 72C-72D. Insulating layers 26 and 28 (like,for example, shallow trench isolation (STI)), may be made of siliconoxide, for example. Insulating layers 26 and 28 insulate cell 550 fromneighboring cells 550 when multiple cells 550 are joined in an array 580to make a memory device as illustrated in FIG. 72A. Insulating layer 26insulate both body region 24 and buried region 22 of adjacent cells (seeFIG. 72C), while insulating layers 28 insulate neighboring body regions24, but not the buried layer 22, allowing the buried layer 22 to becontinuous (i.e. electrically conductive) in one direction (along theII-II′ direction as shown in FIG. 72D).

A region 16 having a second conductivity type, such as n-type, forexample, is provided in substrate 12 and is exposed at surface 14.Region 16 is formed by an implantation process formed on the materialmaking up substrate 12, according to any implantation process known andtypically used in the art. Alternatively, a solid state diffusionprocess can be used to form region 16. Region 16 is continuous(electrically conductive) in the direction along the II-II′ direction(referring to FIG. 72B) and can be used to connect several memory cells550 in parallel like shown in the equivalent circuit representation ofthe memory array 580 in FIG. 73.

A gate 60 is positioned in between the region 16 and insulating layer 26and above the floating body region 24. The gate 60 is insulated fromfloating body region 24 by an insulating layer 62, see FIG. 72C.Insulating layer 62 may be made of silicon oxide and/or other dielectricmaterials, including high-K dielectric materials, such as, but notlimited to, tantalum peroxide, titanium oxide, zirconium oxide, hafniumoxide, and/or aluminum oxide. The gate 60 may be made of, for example,polysilicon material or metal gate electrode, such as tungsten,tantalum, titanium and their nitrides.

Contact between bit line (BL) terminal 74 a and region 16 and contactbetween source line (SL) terminal 72 a and buried layer 22 can be madeat the edge of the parallel connections. Cell 550 further includes wordline (WL) terminal 70 electrically connected to gate 60 and substrateterminal 78 electrically connected to substrate 12. Region 16 (connectedto BL terminal 74) and buried layer 22 (connected to SL terminal 72) canbe used to connect a link of cells 550 in parallel. In a parallelconnection, the voltage applied to the SL terminal 72 and BL terminal 74is about the same for all memory cells 550 (small differences mightoccur due to voltage drop along the bit lines) and the current will onlyflow through the selected memory cell 550.

FIG. 73 shows an equivalent circuit representation of memory array 580,where a plurality of memory cells 550 are connected in parallel. Becauseit is possible to make connections to SL and BL terminals at only theedge of the parallel connections, the number of contacts can be reduced,for example to two contacts, for each parallel connection. No contactsare made to the regions 16 and 22 of the memory cells 550, except forthose cells 550 at the edge of the parallel connections in memory array580. Thus, those cells 550 not at the edge of the parallel connectionsare contactless memory cells. Of course, the number of contacts can beincreased to reduce the resistance of the parallel connections ifdesired.

FIG. 74A shows an equivalent circuit representation of memory cell 550,consisting of a n-p-n bipolar device 30 formed by buried well region 22,floating body 24, and region 16, with a gate 60 coupled to the floatingbody region 24.

A holding operation can be performed by utilizing the properties of then-p-n bipolar devices 30 through the application of a positive back biasto the SL terminal 72 while grounding terminal 74. If floating body 24is positively charged (i.e. in a state “1”), the bipolar transistorformed by BL region 16, floating body 24, and buried well region 22 willbe turned on.

A fraction of the bipolar transistor current will then flow intofloating region 24 (usually referred to as the base current) andmaintain the state “1” data. The efficiency of the holding operation canbe enhanced by designing the bipolar device 30 formed by buried welllayer 22, floating region 24, and region 16 to be a low-gain, (i.e., asnear to 1:1 as practical) bipolar device, where the bipolar gain isdefined as the ratio of the collector current flowing out of SL terminal72 to the base current flowing into the floating region 24.

For memory cells in state “0” data, the bipolar device 30 will not beturned on, and consequently no base hole current will flow into floatingregion 24. Therefore, memory cells in state “0” will remain in state“0”.

An example of the bias conditions applied to cell 550 to carry out aholding operation includes: zero voltage is applied to BL terminal 74, apositive voltage is applied to SL terminal 72, zero or negative voltageis applied to WL terminal 70, and zero voltage is applied to substrateterminal 78. In one particular non-limiting embodiment, about +1.2 voltsis applied to terminal 72, about 0.0 volts is applied to terminal 74,about 0.0 volts is applied to terminal 70, and about 0.0 volts isapplied to terminal 78. However, these voltage levels may vary.

FIG. 74B shows an energy band diagram of the intrinsic n-p-n bipolardevice 30 of FIG. 74B when the floating body region 24 is positivelycharged and a positive bias voltage is applied to the buried well region22. The dashed lines indicate the Fermi levels in the various regions ofthe n-p-n transistor 30. The Fermi level is located in the band gapbetween the solid line 17 indicating the top of the valance band (thebottom of the band gap) and the solid line 19 indicating the bottom ofthe conduction band (the top of the band gap) as is well known in theart. The positive charge in the floating body region lowers the energybarrier of electron flow into the base region. Once injected into thefloating body region 24, the electrons will be swept into the buriedwell region 22 (connected to SL terminal 72) due to the positive biasapplied to the buried well region 22. As a result of the positive bias,the electrons are accelerated and create additional hot carriers (hothole and hot electron pairs) through an impact ionization mechanism. Theresulting hot electrons flow into the SL terminal 72 while the resultinghot holes will subsequently flow into the floating body region 24. Thisprocess restores the charge on floating body 24 to its maximum level andwill maintain the charge stored in the floating body region 24 whichwill keep the n-p-n bipolar transistor 30 on for as long as a positivebias is applied to the buried well region 22 through SL terminal 72.

If floating body 24 is neutrally charged (i.e., the voltage on floatingbody 24 being substantially equal to the voltage on grounded bit lineregion 16), a state corresponding to state “0”, the bipolar device willnot be turned on, and consequently no base hole current will flow intofloating region 24. Therefore, memory cells in the state “0” will remainin the state “0”.

FIG. 74C shows an energy band diagram of the intrinsic n-p-n bipolardevice 30 of FIG. 74A when the floating body region 24 is neutrallycharged and a bias voltage is applied to the buried well region 22. Inthis state the energy level of the band gap bounded by solid lines 17Aand 19A is different in the various regions of n-p-n bipolar device 30.Because the potentials of the floating body region 24 and the bit lineregion 16 are substantially equal, the Fermi levels are constant,resulting in an energy barrier between the bit line region 16 and thefloating body region 24. Solid line 23 indicates, for referencepurposes, the energy barrier between the bit line region 16 and thefloating body region 24. The energy barrier prevents electron flow fromthe bit line region 16 (connected to BL terminal 74) to the floatingbody region 24. Thus the n-p-n bipolar device 30 will remain off.

To perform the holding operation, a periodic pulse of positive voltagecan be applied to the back bias terminals of memory cells 550 through SLterminal 72 as opposed to applying a constant positive bias, therebyreducing the power consumption of the memory cells 550.

Although for description purposes, the bipolar devices 30 in theembodiment of FIGS. 74A through 74C have been described as n-p-ntransistors, persons of ordinary skill in the art will readilyappreciate that by reversing the first and second connectivity types andinverting the relative values of the applied voltages memory cell 550could comprise a bipolar device 30 which is a p-n-p transistor. Thus thechoice of an n-p-n transistor as an illustrative example for simplicityof explanation in FIGS. 74A through 74C is not limiting in any way.

A read operation is described with reference to FIGS. 75-76, wherememory cell 550 b is being selected (as shown in FIG. 75). The followingbias conditions may be applied: a positive voltage is applied to BLterminal 74 a, zero voltage is applied to SL terminal 72 a, a positivevoltage is applied to WL terminal 70 b, and zero voltage is applied tosubstrate terminal 78. The unselected BL terminals (e.g. BL terminal 74b, 74 c, . . . , 74 p in FIG. 75) remain at zero voltage, the unselectedSL terminals (e.g. SL terminals 72 b, 72 c, . . . , 72 p in FIG. 75)remain at zero voltage, the unselected WL terminals (e.g. WL terminal 70a, 70 m, 70 n in FIG. 75) remain at zero voltage, and the unselectedsubstrate terminal 78 remains at zero voltage. Alternatively, a positivevoltage can be applied to the unselected BL terminals connected to theburied layer region to maintain the states of the unselected memorycells.

In one particular non-limiting embodiment, the following bias conditionsare applied to the selected memory cell 550 b: a potential of about +0.4volts is applied to BL terminal 74 a, a potential of about 0.0 volts isapplied to SL terminal 72 a, a potential of about +1.2 volts is appliedto WL terminal 70 b, and about 0.0 volts is applied to substrateterminal 78; while the following bias conditions are applied to theunselected terminals: about 0.0 volts is applied to unselected BLterminals (or +1.2 volts can be applied to SL terminals connected to theburied layer region to maintain the states of the unselected memorycells), about 0.0 volts is applied to unselected WL terminals, and about0.0 volts is applied to unselected substrate terminals.

As shown in FIG. 76, about +1.2 volts will be applied to the gate 60 b,about 0.4 volts will be applied to the region 16 (connected to BLterminal 74 a), about 0.0 volts will be applied to buried layer region22 (connected to SL terminal 72 a), about 0.0 volts will be applied toburied layer 22, and about 0.0 will be applied to substrate 12 ofselected memory cell 550 b. The current flowing from BL terminal 74 a toSL terminal 72 a will then be determined by the potential of thefloating body region 24 of the selected cell 550 b.

If cell 550 b is in a state “1” having holes in the floating body region24, then the memory cell will have a lower threshold voltage (gatevoltage where the transistor is turned on), and consequently willconduct a larger current compared to if cell 550 b is in a state “0”having no holes in floating body region 24. The cell current can besensed by, for example, a sense amplifier circuit connected to BLterminal 74 a.

Alternatively, the read operation can be performed by reversing theconditions applied to BL terminal 74 and SL terminal 72.

A write “0” operation is described with reference to FIGS. 77-78, wherethe following bias conditions are applied: zero voltage to the SLterminal 72 a, zero voltage to the WL terminals 70, negative voltage tothe BL terminal 74 a, and the substrate terminal 78 is grounded. Underthese conditions, the p-n junction between floating body 24 and region16 of the memory cell 550 is forward-biased, evacuating any holes fromthe floating body 24. All memory cells 550 sharing the same BL terminal74 a will be written to state “0”. The unselected WL terminals,unselected BL terminals, unselected SL terminals, and unselectedsubstrate terminals are grounded.

In one particular non-limiting embodiment, about −1.2 volts is appliedto terminal 74 a, about 0.0 volts is applied to SL terminal 72 a, about0.0 volts is applied to terminal 70, and about 0.0 volts is applied tosubstrate terminal 78. The unselected BL terminals 74 (e.g. BL terminals74 b, 74 c, . . . , 74 o, and 74 p) will remain at 0.0 volts, theunselected SL terminals 74 (e.g. SL terminals 72 b, 72 c, . . . , 72 o,and 72 p) will remain at 0.0 volts, and the unselected substrateterminal 78 will remain at 0.0 volts. However, these voltage levels mayvary, while maintaining the relative relationship between the chargesapplied, as described above.

Alternatively the write “0” operation can be achieved by reversing thebias condition applied to BL terminals 74 and SL terminals 72.

An alternative write “0” operation that allows for individual bitwriting is shown in FIGS. 79-80, and can be performed by applying anegative voltage to BL terminal 74 a, zero voltage to SL terminal 72 a,zero voltage to substrate terminal 78, and a positive voltage to WLterminal 70. Under these conditions, a positive voltage will be appliedto the gate of the selected memory cell (e.g. memory cell 550 b in FIGS.79-80) and consequently the floating body 24 potential will increasethrough capacitive coupling from the positive voltage applied to the WLterminal 70. As a result of the floating body 24 potential increase andthe negative voltage applied to the BL terminal 74 a, the p-n junctionbetween 24 and region 16 is forward-biased, evacuating any holes fromthe floating body 24. To reduce undesired write “0” disturb to othermemory cells 550 in the memory array 580, the applied potential can beoptimized as follows: if the floating body 24 potential of state “1” isreferred to V_(FB1), then the voltage applied to the selected WLterminal 70 is configured to increase the floating body 24 potential byV_(FB1)/2 while −V_(FB1)/2 is applied to BL terminal 74 a.

In one particular non-limiting embodiment, the following bias conditionsare applied to the memory cell 550: a potential of about 0.0 volts to SLterminal 72 a, a potential of about −0.2 volts to BL terminal 74 a, apotential of about +0.5 volts is applied to selected WL terminal 70 b,and about 0.0 volts is applied to substrate terminal 78; while about 0.0volts is applied to unselected BL terminals 74, about 0.0 volts isapplied to unselected SL terminals, about 0.0 volts is applied tounselected WL terminal 70, and about 0.0 volts is applied to unselectedterminal 78. Alternatively, a positive voltage, for example of +1.2volts, can be applied to unselected SL terminals 72 connected to theburied layer region 22 to maintain the states of the unselected memorycells. FIGS. 79-80 show the bias condition for the selected andunselected memory cells in memory array 580 where memory cell 550 b isthe selected cell. However, these voltage levels may vary.

Alternatively, the write “0” operation described above can be achievedby reversing the bias condition applied to BL terminals 74 and SLterminals 72.

An example of the bias condition of the selected memory cell 550 b underband-to-band tunneling write “1” operation is illustrated in FIGS. 81and 82. A negative bias is applied to the selected WL terminal 70 b,zero voltage is applied to the SL terminal 72 a, and a positive biasapplied to the BL terminal 74 a, while the substrate terminal 78 isgrounded. This condition results in electrons flow to the BL terminal 74a, generating holes which subsequently are injected to the floating bodyregion 24.

In one particular non-limiting embodiment, the following bias conditionsare applied to the selected memory cell 550 b: a potential of about 0.0volts is applied to SL terminal 72 a, a potential of about +1.2 volts isapplied to BL terminal 74 a, a potential of about −1.2 volts is appliedto the selected WL terminal 70 b, and about 0.0 volts is applied tosubstrate terminal 78; while the following bias conditions are appliedto the unselected terminals: about 0.0 volts is applied to unselected BLterminals (e.g. BL terminals 74 b, 74 c, . . . , 74 o, and 74 p in FIG.81), about 0.0 volts is applied to unselected SL terminals (e.g. SLterminals 72 b, 72 c, . . . , 72 o, and 72 p in FIG. 81), a potential ofabout 0.0 volts is applied to unselected WL terminal 70 (e.g. WLterminals 70 a, 70 m, and 70 n in FIG. 81), and about 0.0 volts isapplied to substrate terminal 78. A positive voltage of about +1.2 voltscan alternatively be applied (either continuously, or intermittently inpulse fashion as described above, to reduce power consumption) tounselected SL terminals connected to the buried layer region 22 tomaintain the states of the unselected memory cells). FIGS. 81-82 showthe bias conditions for the selected and unselected memory cells inmemory array 580 where memory cell 550 b is the selected cell. However,these voltage levels may vary.

An example of the bias conditions on the selected memory cell 550 bunder impact ionization write “1” operation is illustrated in FIGS.83-84. A positive bias is applied to the selected WL terminal 70 b, zerovoltage is applied to the SL terminal 72 a, a positive bias is appliedto the BL terminal 74 a, and the substrate terminal 78 is grounded.These conditions result in a lateral electric field sufficient togenerate energetic electrons, which subsequently generate electron-holepairs, followed by hole injection to the floating body 24 of theselected memory cell (e.g. cell 550 b in FIGS. 83-84).

In one particular non-limiting embodiment, the following bias conditionsare applied to the selected memory cell 550 b: a potential of about 0.0volts is applied to SL terminal 72 a, a potential of about +1.2 volts isapplied to BL terminal 74 a, a potential of about +1.2 volts is appliedto the selected WL terminal 70 b, and about 0.0 volts is applied tosubstrate terminal 78; while the following bias conditions are appliedto the unselected terminals: about 0.0 volts is applied to unselected BLterminals 74 (e.g. BL terminals 74 b, 74 c, . . . , 74 o, and 74 p inFIG. 83), about 0.0 volts is applied to unselected SL terminals 72 (e.g.SL terminals 72 b, 72 c, . . . , 72 o, and 72 p in FIG. 83), a potentialof about 0.0 volts is applied to unselected WL terminals 70 (e.g. WLterminals 70 a, 70 m, and 70 n in FIG. 83), and about 0.0 volts isapplied to substrate terminal 78. A positive voltage of about +1.2 voltscan alternatively (either continuously, or intermittently in pulsefashion as described above, to reduce power consumption) be applied tounselected SL terminals 72 connected to the buried layer region 22 tomaintain the states of the unselected memory cells). FIGS. 83-84 showthe bias conditions on the selected and unselected memory cells inmemory array 580 (with memory cell 550 b as the selected cell). However,these voltage levels may vary.

Alternatively, the write “1” operations under band-to-band tunneling andimpact ionization mechanisms described above can be achieved byreversing the bias conditions applied to BL terminals 74 and SLterminals 72.

The array 580 may be constructed from a plurality of planar cells, suchas the embodiments described above with reference to FIGS. 74C and 74D,or, alternatively, may be constructed from fin-type, three-dimensionalcells. Other variations, modifications and alternative cells may beprovided without departing from the scope of the present invention andits functionality.

From the foregoing it can be seen that with the present invention, asemiconductor memory with electrically floating body is achieved. Thepresent invention also provides the capability of maintaining memorystates or parallel non-algorithmic periodic refresh operations. As aresult, memory operations can be performed in an uninterrupted manner.While the foregoing written description of the invention enables one ofordinary skill to make and use what is considered presently to be thebest mode thereof, those of ordinary skill will understand andappreciate the existence of variations, combinations, and equivalents ofthe specific embodiment, method, and examples herein. The inventionshould therefore not be limited by the above described embodiments,methods, and examples, but by all embodiments and methods within thescope and spirit of the invention as claimed. While the presentinvention has been described with reference to the specific embodimentsthereof, it should be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the true spirit and scope of the invention. In addition,many modifications may be made to adapt a particular situation,material, composition of matter, process, process step or steps, to theobjective, spirit and scope of the present invention. All suchmodifications are intended to be within the scope of the claims appendedhereto.

That which is claimed is:
 1. An integrated circuit comprising: a link orstring of semiconductor memory cells, wherein each said semiconductormemory cell comprises: a floating body region for storing chargeindicating a state of said semiconductor memory cell; and a back-biasregion; wherein applying a voltage to said back-bias region results inat least two stable floating body charge levels; wherein said link orstring comprises at least one contact configured to electrically connectsaid semiconductor memory cells to at least one control line; wherein anumber of said at least one contact is the same as or less than a numberof said semiconductor memory cells in said link or string; and a controlcircuitry configured to apply said voltage to said back-bias region. 2.The integrated circuit of claim 1, wherein said number of said at leastone contact is less than said number of said semiconductor memory cells.3. The integrated circuit of claim 1, wherein said semiconductor memorycells are connected in series.
 4. The integrated circuit of claim 1,wherein said semiconductor memory cells are connected in parallel. 5.The integrated circuit of claim 1, wherein said integrated circuit isfabricated on a bulk silicon substrate.
 6. The integrated circuit ofclaim 1, wherein said number of said at least one contact is two.
 7. Theintegrated circuit of claim 1, wherein said semiconductor memory cellsfurther comprise first and second conductive regions interfacing withsaid floating body region.
 8. The integrated circuit of claim 1, whereineach said semiconductor memory cell further comprises a gate insulatedfrom said floating body region.
 9. The integrated circuit of claim 1,wherein at least one of said semiconductor memory cells is a contactlesssemiconductor memory cell.
 10. The integrated circuit of claim 9,wherein a majority of said semiconductor memory cells are contactlesssemiconductor memory cells.
 11. An integrated circuit comprising: a linkor string of semiconductor memory cells, wherein each said semiconductormemory cell comprises: a floating body region for storing charge; and aback bias region; wherein applying a voltage to said back-bias regionresults in at least two stable floating body charge levels; wherein saidlink or string comprises at least one contact configured to electricallyconnect said semiconductor memory cells to at least one control line;wherein a number of said at least one contact is the same as or lessthan a number of said semiconductor memory cells in said link or string;and wherein said at least one control line is connected to a readcircuitry; and a control circuitry configured to apply said voltage tosaid back-bias region.
 12. The integrated circuit of claim 11, whereinsaid number of said at least one contact is less than said number ofsaid semiconductor memory cells.
 13. The integrated circuit of claim 11,wherein said semiconductor memory cells are connected in series.
 14. Theintegrated circuit of claim 11, wherein said semiconductor memory cellsare connected in parallel.
 15. The integrated circuit of claim 11,wherein said integrated circuit is fabricated on a bulk siliconsubstrate.
 16. The integrated circuit of claim 11, wherein said numberof said at least one contact is two.
 17. The integrated circuit of claim11, wherein said semiconductor memory cells further comprise first andsecond conductive regions interfacing with said floating body region.18. The integrated circuit of claim 11, wherein each said semiconductormemory cell further comprises a gate insulated from said floating bodyregion.
 19. The integrated circuit of claim 11, wherein at least one ofsaid semiconductor memory cells is a contactless semiconductor memorycell.
 20. The integrated circuit of claim 19, wherein a majority of saidsemiconductor memory cells are contactless semiconductor memory cells.